Favorite and Least Favorite Pokemon by Generation

gen one ? eevee and abra
gen two ? typhlosion and raikou
gen three ? aggron and loudred
gen four ? leafeon and snover
gen five ? reuniclus and palpitoad
gen six ?sylveon and avalugg

no opinion of the gen7 pokemon as of yet :>

Gen I:
Favourite - Gengar
Least - Snorlax

Gen II:
Favourite - Ariados
Least - Ursaring

Gen III:
Favourite - Swellow
Least - Slaking

Gen IV:
Favourite - Weavile
Least - Ambipom

Gen V:
Favourite - Vanilluxe
Least - Darmanitan

Gen VI:
Favourite - Klefki
Least - Barbaracle

Gen VII:
Favourite - Araquanid
Least - Bewear

Gen I
Favourite: Charizard
Least favourite: Mr. Mime

Gen II
Favourite: Quilava
Least favourite: Miltank

Gen III
Favourite: Absol
Least favourite: Shiftry

Gen IV
Favourite: Gallade
Least favourite: Bibarel

Gen V
Favourite: Herdier
Least favourite: Ferroseed

Gen VI
Favourite: Braixen
Least favourite: Diggersby

Gen VII
Favourite: Decidueye
Least favourite: Gumshoos

Hmmm never thought about my favorites (least) by gen:

Gen 1:
Favorite: Hitmonchan - late bloomer, has really blossomed into one of my favorite all time pokemon
Least: Tentacool - just....no

Gen 2:
Favorite: Totodile, first starter i ever chose
Least: unown - I appreciate the lore but I just look at them and well, I just don't like them

Gen 3:
Favorite: Poochyena/Corphish, Mainstays on my hoenn runs
Least: Lileep, Never been a big fan of the fossil mons but this is the worst of them for me

Gen 4:
Favorite: Buizel, my all time favorite; honorable mention to Infernape
Least: Gastrodon, Not a huge fan of monster globs

Gen 5:
Favorite: Golurk, Gen 5 has grown a lot on my the last few years, this mon takes the cake
Least: Amoonguss, exact opposite of Pokemon I like to use, honorable mention to entire Gothita line

Gen 6:
Favorite: Greninja, only starter line I love more is the Chimchar line, love its place in Pokemon history now
Least: Aromatisse, i don't see a bit of appeal in this mon

Gen 7:
Favorite: Tsareena/Lycanroc-Midday, can't decide between the two, about to become the first two Pokemon I've ever gotten to lvl 100
Least: Oricorio(s), I don't like any of these birbs, bother me to no end

Kanto:
Favorite - Arcanine, I didn't always like Arcanine, but when I met a close friend who liked it, I ended up liking it.
Least - Mr. Mime, terrible design. Name is stupid.

Johto:
Favorite - I can't chose between Heracross, Noctowl, Umbreon, Donphan and Gligar, but I would probably have to say Donphan.
Least - Xatu - although it matches Johto's vibe well, I'm just not a fan of the humanoid like appearance Natu has a 100% better design.

Hoenn:
Favorite - Flygon, has been one of my favorite design forever. Wish it was a Dragon/Bug though.
Least - Spinda, unique concept, just not a fan.

Sinnoh:
Favorite - Empoleon, favorite starter of all time.
Least - Magmortar - never been a fan of its line.

Unova:
Favorite - Krookodile, when I first saw Sandile, I fell in love with the design. Just got better as it grew. Kinda wish it had a better red or something though.
Least - Gothitelle line, I just hate the design.

Kalos:
Favorite - Gogoat, one of my favorite non starting grass type pokemon of all time. I also really love Pumkaboo due to the Halloween theme.
Least - Barbaracle line, I just hate the line with a passion. The design is pure uglyness.

Alola:
Favorite - Mudsdale and Decidueye, out of all Alolan pokemon, those are the only 2 that blew me away.
Least - Gumshoos line, I just hate it. If the teeth weren't as bad, I don't think it would be a problem, but the teeth just kill the design.

Alolan Forms: Doing Alolan forms because they aren't really Gen 1 or Gen 7.
Favorite - Ninetails, love it.
Least - Dugtrio, Looks basically the same as normal, just with rock star hair, which is a bit much. Ampharos looked badass, this took adding hair too far.

again love how pokemon like Rhyperior and Magmortar give so much salt xD

anyway not posting about gen 7, but:

Gen 1 - Gengar, Snorlax, Pidgeot / Jynx, Mr. Mime, Geodude
Gen 2 - Crobat, Feraligatr, Ursaring / Dunsparce, Ditto, Espeon (fuck Baton Pass)
Gen 3 - Milotic, Exploud, Swellow / Clamperl, Deoxys, Ninjask, Plusle and Minun
Gen 4 - Weavile, Rhyperior, Staraptor / Arceus, Glaceon, Bronzor, Pachirisu
Gen 5 - Excadrill, Emboar, Victini / Vanillish, Emolga, Scolipede
Gen 6 - Greninja, Talonflame, Goomy, Goodra / Slurpuff, Volcanion

It's usually hard for me to limit myself to one of each Pokemon per gen, so if you were to ask me the same question a week from now, half of my answers would probably change :p

Gen I (Kanto):
Favorite: Butterfree. Not just my favorite from the original 151, but my favorite Pokemon overall.
Least Favorite: Tentacool. The Zubat of the sea, but at least Zubat eventually turns into something interesting.

Gen II (Johto):
Favorite: Azumarill. It took me many years for me to realize how great Azumarill was, and the addition of Fairy typing boosted my love for it.
Least Favorite: Hitmontop. I don't really hate it, I just wish that Tyrogue/Hitmontop were unrelated to Hitmonlee/Hitmonchan.

Gen III (Hoenn):
Favorite: Sceptile. Lots of great choices for Hoenn, but I have to stick with my OG Sapphire starter.
Least Favorite: Nosepass. It's just a really meh Pokemon to it, and I only dislike it because of its evolution.

Gen IV (Sinnoh):
Favorite: Froslass. Again, a lot of good Pokemon to choose from, but I've always loved Froslass' design & typing.
Least Favorite: Probopass. A very unnecessary evolution, and one of the few Pokemon I'd actually consider ugly.

Gen V (Unova):
Favorite: Hydreigon. Love the concept/typing of Hydreigon, and probably my favorite pseudo-legendary.
Least Favorite: Roggenrola. My least favorite Pokemon. Has the creativity of a 7 year old's first Fakemon.

Gen VI (Kalos):
Favorite: Hawlucha. Didn't know how badly I wanted a luchador Pokemon until we finally got one!
Least Favorite: Barbaracle. Not a bad idea, but poor execution. Another one of the few Pokemon I'd consider ugly.

Gen VII (Alola):
Favorite: Decidueye. Love the whole line, and would probably put it as one of my top 3 favorite starters overall.
Least Favorite: Bruxish. I don't hate it, but I think it could they could've toned its design down a few notches.

Gen 1
Faves: Starmie Arcanine Victreebel Vaporeon Dragonair I'll stop here
Least fave: Lickitung
Gen 2
Faves: Ampharos,
Least: Generally the babies except Elekid but especially Pichu

Gen 3
Faves: Sceptile Flygon Beautifly Gardevoir
Least: gulpin line

Gen 4 (less familiar with this one)
Faves: Lucario,
Least: Gen 1 evolutions: electivite, magmortar, rhyperior, especially Lickilicki (exceptions for tangrowth and others)

Gen 5
I'll get back to it

Gen 6:
Faves: Honedge line, chesnaught, talonflame among others
Least faves: SWIRLIX, SLURPUFF hate these things

Gen 7
Faves: I'll get back to it
Least: Bewear

I was actually thinking of a similar thing and was going to make a post ... glad I decided to search first XD
I was thinking of making a team with my favorite pkmn from each gen (mulligan when there's none or a replacement because we've past 6 gens).
anyway for me:

Gen 1
Favourite: Lapras ... idk it's a pkmn that comes back often which just made me love it over time. I don't really have a favorite for gen 1 otherwise ... maybe Mewtwo
Least favourite: fearow ... I just never liked it XD

Gen 2
Favourite: Celebi ... just a good looking pokemon imo.
Least favourite: Snubbull ... I just find it an ugly pokemon ... I'm sorry XD

Gen 3 my fav gen, has several pkmn I like but I suppose:
Favourite: Gardevoir and Absol both share that spot. Gardevoir is an overall interesting pokemon imo, Absol just fits me XD
Least favourite: Swallot ... just looks kind of lame, kind of like a Muk pumped with botox to look tight instead of the sloppy mess Muk is XD

Gen 4
Favourite: Lucario ... I started to like him through the tcg (Korrina FA just looked amazing and it snowballed a bit)
Least favourite: Drapion ... there are actually quite a few, mostly the evolutions from previous (gen 1) pkm but Drapion is just one of those pokemon that always stood out for being awkward imo.

Gen 5
Favourite: Lilligant, what can I say, I'm a sucker for good looking pokemon XD
Least favourite: Garbodor ... it's a trashback, literally

Gen 6
Favourite: Diancie ...
Least favourite: Chesnaught and Delphox ... both look bad but at least the pre-evolutions of Delphox look good

Gen 7
Favourite: Magearna .... at this point I think it's starting to become rather obvious what I like about pokemon XD
Least favourite: All of the Ultra beasts (ignoring the jelly fish)

After this, I don't think I'll stick to the idea of making a team of my favorite from each gen XD

Gen 1
Favourite: Gengar
Least Favourite: Ratata

Gen 2
Favourite: Crobat
Least Favourite: Smeargle

Gen 3
Favourite: Camerupt
Least Favourite: Zigzagoon

Gen 4
Favourite: Honchkrow
Least Favourite: Arceus

Gen 5
Favourite: Haxorus
Least Favourite: Throh

Gen 6
Favourite: Dragalge
Least Favourite: Quilladin

Gen 7
Favourite: Araquanid
Least Favourite: Alolan Diglett

Hmm I gotta think good about this.

Gen I:
Favourite: Zapdos (naturally).
Least favourite: /

Gen II:
Favourite: I'm bad at choosing. Flaaffy, Dunsparce, Umbreon, and Raikou.
Least favourite: Stantler is very forgettable.

Gen III:
Favourite: Shedinja.
Least favourite: Makuhita aka Satan himself.

Gen IV:
Favourite: Arceus
Least favourite: Ambipom, I feel like it's a redundant evolution.

Gen V:
Favourite: Gen V has a lot of good Pokémon, but I don't feel strongly towards any of them specifically. Maybe Samurott.
Least favourite: Whimsicott because it's a bitch, and Scraggy/Scrafty because I keep forgetting its typing.

Gen VI:
Favourite: Honedge because I love swords.
Least favourite: A lot of designs in this generation are just bad, but Binacle/Barbaracle is the very worst.

Gen VII:
Favourite: Rowlet, Lycanroc-Dusk, Mimikyu, Solgaleo.
Least favourite: Crabrawler/Crabominable, I don't even wanna catch/train these for dex entries...

Gen 1:
Favorite: Mewtwo. Still my favorite Pokemon. Both Megas are equally awesome as well.
Least Favorite: Seaking. I don't hate it, but compared to the other Gen 1 Pokemon, it's very forgettable.

Gen 2:
Favorite: Typhlosion. My first Pokemon and Starter. So many fond memories of destroying Johto with him at my side.
Least Favorite: Wobbuffet. Four words: Shadow Tag, Destiny Bond.

Gen 3:
Favorite: Gardevoir. My second favorite Pokemon. Both adorable and powerful. Gen 6 made it even better.
Least Favorite: Chimecho. Finding a Pokemon with an encounter rate of only 2%, and it's not even that good? Also, why did this of all things get a pre-evo in Gen 4?

Gen 4:
Favorite: Giratina. I just really like the antimatter dragon. Especially its Origin Forme.
Least Favorite: Chatot. I'm just not a fan of it.

Gen 5:
Favorite: Reshiram. I'm a big fan of Blue-Eyes White Dragons. Such an amazing design and a great type as well.
Least Favorite: Emolga. My least favorite Pika clone, and I dislike all Pika clones.

Gen 6:
Favorite: Delphox. My favorite starter since Typhlosion. I love mages and foxes. Its design is both adorable and badass. Plus, it even has my two favorite types.
Least Favorite: Greninja. Overrated, gets preferential treatment from Game Freak while the other Kalos starters get ignored, hideous design (in my opinion), and the fact that it's constantly shoved in my face makes the entire line my least favorite Pokemon of all.

Gen 7:
Favorite: Incineroar. It looks so freaking badass. I don't care what anyone says, I'm glad it's bipedal. Also, Malicious Moonsault is awesome.
Least Favorite: Togedemaru. I'm just not a fan of Pikaclones. Also, Mimikyu completely overshadows this.

Kanto
favorite: Ninetales, Arcanine, Eevee, Jolteon, Bulbasaur
Least favorite: Mrmime
Johto
Favorite: Houndoom, espeon, umbreon, hooh, lugia
Least favorite: Celebi
Hoenn
favorite: Mightyena
Least favorite: Milotic
Sinnoh
favorite: Dialga, Giratina
least favorite: Lucario
Unova
favorite: Reshiram
least favorite: pignite
Kalos
favorite: zygarde, sylveon, dedenne
least favorite: Delphox
Alola
favorite: Solgaleo, Rockruff
least favorite: Toucannon.

Hard choices, least favorite doesn't necessarily mean I dislike them though, just that they're at the bottom in comparison to other pokemon

Kanto
Favorite: Snorlax, Hypno
Least favorite: Mewtwo

Johto
Favorite: Espeon, Typhlosion
Least favorite: N/A (Ledian)

Hoenn
Favorite: Torchic (don't like Blaziken or Combusken though), Exploud, Flygon
Least favorite: Blaziken, Gardevoir

Sinnoh
Favorite: Chatot, Infernape
Least favorite: Lucario 100%

Unova
Favorite: Samurott, Lilligant, Leavanny
Least favorite: Ferrothorn, Landorus, Thundurus, Tornadus

Kalos
Favorite: Delphox, Klefki
Least favorite: Greninja

Alola
Favorite: Primarina, Shiinotic
Least favorite: Celesteela, Pheromosa, Buzzwole (for robbing Heracross and Skarmory of their unique typings)

Sure, why not. Trying to limit myself to just one per gen per category, although I could easily dip into three or five per generation.

Kanto
Favorite: Articuno
Least favorite: Arcanine

Johto
Favorite: Misdreavus
Least favorite: Snubbull

Hoenn
Favorite: Latias
Least favorite: Treecko

Sinnoh
Favorite: Bastiodon
Least favorite: Lucario

Unova
Favorite: Meloetta
Least favorite: Zoroark

Kalos
Favorite: Klefki. Fight me.
Least favorite: Greninja

Alola
Favorite: Celesteela
Least favorite: Lycanroc Midnight