My friends and I actually have a bet going on. I'm betting that within two more generations, every new pokemon will be an indistinguishable puff ball, but they'll all have different color variations.
What? Your pink puffball is evolving into...mauve puffball!
I am totally against the cute-ifying of pokemon. They get cuter, and stupider, and more /gag-me looking with each new generation. I'm not saying the first was perfect by any means, but the 'cool' ones are getting to be fewer and far between.
I think you're just getting older, to be honest. I had a lot of issues digesting the newer gens too, for similar reasons. But you know, they're not all that bad. Just relax and accept it. The vast majority of gen1 pokies were excruciatingly cute and often stupid too (psyduck as the most notable example). All gens have cute ones (Pikachu - Sentret - Plusle etc), weird ones (Staryu and Magnemite - Dunsparce - Bronzor etc) and epic looking legendary/dragon ones (Dragonite, all the way up to Hydreigon - Mewtwo, Raikou, Rayquaza, etc.). But gen1 will probably have a special place in your heart because of the magic of it when you were a kid, and the newer ones lack that for you. And that's normal, but that doesn't make the newer gens worse.
The anime work more closely together with the games now and that's been really noticable. That was entirely different in gen1 and to a lesser extent gen2 also, which is easily notable by how the sprites differ from the anime ones (Ghastly f/ex). I think that has definitely influenced the newer pokies' looks. Plus, the show is aimed mostly at younger kids, which you were once, during gen 1, too - so please consider that before bashing newer gens. You're getting older.
It's been a long time, and I remember basing my thoughts on each from the anime, where you got to actually see them in action. All I know now, is that I got a small plush of Oddish, back when I think Burger King was giving them out, over 10 years ago.
And there's just the adorable ones. Mew, Dratini, the three starters, Seel, Growlithe, Jigglypuff. Really didn't pay much attention to which ones I used each time I played.
I've always had a soft spot for Meowth. I suppose part of the reason is because I love cats and the other part of the reason is that I have fond memories of watching the Pokémon show as a kid and cheering Team Rocket on. A bit embarrassing to admit, though!
Play since Gen I, but honestly Gen V has the highest amount of favourite pokemon for me.... call me crazy, but it is a gen that is very... divided, it has the UGLIEST pokemon, but it also has the prettiest and most awesome.
Special note would be for other 2 pokemon i like
"smashy" and "pouncy" (yes im 25 and call them that, fu! <3)