Don't Press B! ...or?

[Tora]

Chicorita is easily my favorite starter. Even though, out of the fully evolved 2nd gen starters, Meganium is still my favorite. There's just something about that gen. The starters are all super cute, but I don't like their final forms as much as their basic form. In gen 3, I prefer Torchic and Grovyle over Blaziken and Sceptile. Torchic has to be the cutest chicken I've ever seen and Grovyle on the other hand is so much cooler. Sceptile is too fat and unelegant.

Just like Dragonair is more elegant and beautiful than Dragonite. I also prefer Haunter over Gengar, because it looks better, especially in early gens, when it still had those glowing hands. And I prefer Kadabra, but that has probably more to do with the fact that I used it a lot in Silver and I didn't have anyone to trade with.

While I like all of the Eeveelutions, my favorite Eevee form is still Eevee, so I have one as the inofficial "king" of my competitive pack. ;)

Like some others already mentioned, many of the 4th gen evolutions for already existing Pokémon are not that great, especially Lickilicky, Probopass, Tangrowth.

And as for the newest generation... my egg hatcher/fly user is Fletchinder, not Talonflame. I played through the game with Talonflame, but caught a new one after the League specifically to be almost constantly on my team. Not so much because of the design, I actually like them both. No, it's that super awesome/cute cry that made me fall in love with the middle stage. <3

Also, if I ever get a shiny Ponyta, I won't evolve it. Letting that lovely mane of blue flames turn into a dull grey? Never!

 

[Khoshi]

Some I prefer pre-evolved due to statistical benefits, like Dusclops. Dusclops becomes rather scary when you slap an Eviolite on it.

Others, I prefer appearance, and movepools too. Growlithe embodies both of those points for me. Yes, I realise you don't need a B button for Growlithe, but I prefer holding off on a Fire Stone so I can both appreciate Growlithe's cute appearance, and its movepool.

Sometimes, I want things to evolve as quickly as possible, like Eevee. God, I hate Eevee. I try to chuck stones at it to evolve it immediately, or I take the time to raise happiness or affection as soon as I obtain one. I will never keep an Eevee as an Eevee unless I'm breeding them.

 

[AdamN]

I dislike the 1st and 2nd evolutions of ALL grass type starters.
Actually I can't think of any 1st evolution of a starter that I particularly enjoy.

 

[IronChainDragon]

I have a tendency to keep my starters unevolved for as long as possible. Also, for whatever reason, I prefer Kirlia to either of its evolutions.

 

[KorpiklaaniVodka]

I like how this is a thread where Pokemon such as Dragonite, Raichu, Rhyperior and Magnezone get shat on while no one mentions Politoed. Despite it having Drizzle, it looks so awkward when placed next to Poliwag, Poliwhirl and Poliwrath. I don't even need to explain. Just look at them.

 

[Tamashi_Seishiro]

Munchlax, and Pikachu (cuteness overload!)

 

[Aether★]

Magneton, I always make sure to use Eviolite on this one. My favorite mid-evo pokemon and electric type.

 

[Light_Archer]

Like a lot of people, I prefer Pikachu over Raichu, Rhydon over Rhyperior, that sort of thing... I guess it's because I played the older games a lot. :/

 

[Crystal Berry]

Chansey, Dusclops, P2, Pikachu.

 

[rebelrabbit]

When I originally played Gale of Darkness, I was never able to bring myself to evolve my little Teddiursa (who I named Benny). Even though his evolved form turns into a self-healing behemoth that one-shots literally everything, I just couldn't let his evolve.
And I can't megavolve Gengar, it just isn't the same.