Has your favorite Pokémon changed over time?

Yes, it has changed many times. I don't remember all of them, but when I got first into Pokémon, I was a fan of Gallade. My favorite Pokémon is Hydreigon currently.

Vulpixs and Ninetales are still my top favourite since I was a kid playing RBY, adding their Alolan forms help a lot too.

Not since Shinx came along! It has been my #1 favourite and mascot Pokémon for... hmm, ten years now? And I doubt that will change! The closest to rival Shinx has been Helioptile because I find it so darn cute, ahaha.

Before then, I think it was Eevee or Vaporeon, with Persian close behind. That's only because I skipped through Johto and Hoenn!

Back then I don't quite have definite favorites, even though I do have soft spot on Eevee and later on Shaymin. Years after, I begin to be curious about Victini (iirc around when Pokémon Black/White games are announced), and some certain events like how it being my first Critical Capture makes me like it even more, to the point Victini becomes my main favorite Pokémon, and it hasn't changed ever since. As for now, even though I may have more fave Pokémon on my list, Victini would still fill the spot of my flagship favorite Pokémon.

I started watching the anime and didn't have any real favourite, then in my first game (Gold) I chose Chikorita and that evolution line has been among my favourites ever since; I still think my absolute favourite Pokémon is Meganium, even though there have been others that have been contenders and were my favourites for some time (Dewgong, Politoed, Blaziken, Kyogre, Combee, Lopunny Toxicroak, Lilligant, Litwick, Mandibuzz) and now I have an almost joint-favourite in Primarina.
Also it's not a standalone Pokémon but Mega Altaria rounds up the top 3 (and it's still among my favourites even without the Mega).

At first I liked Blastoise the most, in every Pokemon game i used to choose Squirtle as my starter which will become Blastoise in future.

And when Pokemon XYZ Anime came and when I saw the last evolution of Froakie which is Greninja, it looked way cooler than any other Pokemon till now I've seen.(except Infernape, because I love Water types). And also after Frogadier, the Greninja which we get is Water as well as a Dark type. Who doesn't like Dark type?? Because till Greninja was introduced the most beloved Dark type was Lucario in my opinion!!! So here Greninja became my favourite.

And at last Gardevoir, because of the new Fairy type, plus Psychic type. And all must have already known that why people love Gardevoir ;)

When I was younger and was in Pokemon for a little bit, I don't think I even had a favourite Pokemon. After I was reintroduced into the series, it was Houndoom because I loved dogs and it had a slick design. Cue Gen 5 and I just fell in love with Scrafty after 6 months of BW's NA's release date and I don't see that changing anytime soon.

While my #1 doesn't change, my top 10 sometimes fluctuates.

Raichu, pidgeot, butterfree and charzard have pretty much been my favourite pokemon since the beginning and still are but a few others have joined like Feraligater gen 2,swampert in gen 3,leafeon and mamoswine gen 4, sawk, throh and braviary gen 5, greninja and talonflame gen 6 and gen 7 I favour incineroar and toucannon

When I was much younger, I only knew about the Kanto region for the most part. I watched the Indigo League anime and I owned a copy of Fire Red (which I know is technically Generation 3, but it primarily had Gen 1 Pokémon for the most part.)

Back then, my favorite was initially Magmar, simply because it looked cool and I liked fiery things, but when I first encountered Mewtwo in Fire Red, it instantly became my favorite for the longest time.
That is, until I got Pokémon Diamond, it was then I started learning new Pokémon, and for a brief time, Dialga was my favorite, but I only knew about the two games back then, I didn't have the internet.
Around when Gen 5 came out, I got some huge book of all Pokémon across the 5 generations for Christmas, and I've discovered a lot.

It was also there I found out about Deoxys, and I was extremely intrigued with the idea of a Pokémon that's just a straight-up alien.
Whenever I got access to the internet, I'd do research on this Pokémon, and it quickly became my all-time favorite, almost as if I were connected to it in some ways.
Especially in the Destiny Deoxys movie. That's definitely my favorite of the Pokémon movies.

Definitely not the same now. I used to be the typical Charizard and "choose fire starters because fire" kid growing up with the games. Now it's Eelektross and Gourgeist. Charizard and Kanto as a whole has been ruined for me the past few years. But Mega X is still cool. I'm more of a grass type person now

Mine was Squirtle, but now it's probably Bulbasaur (even though I never chose Bulbasaur as a starter). Pikachu is always a joint favourite.

Blastoise was one of the first Pokémon I ever saw. Some classmates had these fabric Pokémon that inverted from poke balls to Pokémon, and Blastoise was one of them. I liked it, and consequently picked it as my starter when I got Red. It's been my favorite ever since, and I've never had any urge to deviate from that.

Most of my favorites have been set in stone for years (Pikachu as #2, etc.). I've liked some new Pokemon, but I guess I'm fairly consistent in my tastes. The same goes for a lot of my other favorites in life (color, etc.).

Yeah, it was gyarados at some point but he's probably not even my favorite gen 1 mon now (i like nidoking, victreebel and starmie better I think)

Indeed, back when I first started getting into Pokemon around early Gen IV, I had Lucario as my #1 favourite for a while. Always thought he was pretty cool, and 'cool' was like the big thing for me back in the day.

Around early Gen VI, I started to transition away from the 'cool' and more towards the 'cute/girly', and Gardevoir became my new favourite for a bit. Then finally at some point I got into OR/AS and discovered Lopunny's mega evolution, and she's been my #1 ever since. ^^

Yeah, it constantly changes and often gravitates towards what's being showcased in the anime. During Gen V I didn't care much for Emolga, Excadrill or Scraggy, now they're certainly my some of my favourites.

Miltank fan since 2001

My favorite Pokemon, Dawn Wings Necrozma, was only created two games ago, so yes. Before Gen 7, it was Victini. Between Black & White first being revealed and me doing the Liberty Garden event in my game (which was what made me love Victini), it was Oshawott. Before Oshawott...I don't think I had one.

All 3 (4?) Pokemon are still very important to me; I tend to call DW Necrozma my current favorite, Victini my old favorite, and Oshawott my mascot (like how Ash has Pikachu, Dawn has Piplup, Iris has Axew, etc.). c:

Sneasel was my most favorite Pokémon until Gen VII, when I met Charjabug.

And I hope Charjabug stays my favorite.

Ninetales has always and will always remain on top.

Some of my other all-time favourites such as Beautifly, Lopunny, Gardevoir, and Glaceon also have remained on the top of my list.

So for a while it was whatever starter I had, wasn't too picky
Around gen 4 I was into Golduck and its design, Unova came and Axew happened...
then for some reason I settled on Lucario. Dunno why. Liked the design