i'm in your conscience
My original favorite Pokemon was Eevee. It was the first card I received, so when I think of gen I favorites, Eevee is always first. I also like it's evolutions a ton. Other Pokemon this gen I like are Venonat, Charmander, and Articuno.
My all time favorite Pokemon is Umbreon, and it's also from gen II. So fitting for this thread lol. I loved it ever since I saw it in Pokemon Stadium 2. I also like Espeon, Jumpluff, Quilava, Smeargle, and Aipom.
As for least favorites, I'm not a fan of Pikachu at all. I used to really, really hate it as a kid, but it's at least tolerable now. I have a plushie Pikachu that's the cutest Pikachu I've ever seen. But I generally just dislike Pikachu. Not as much as when I was 7 though lol. I don't really like some of the more bland or strange Pokemon gen I offers though. Not a huge fan of Lickitung. I really hate its evo, but that's a topic for another generation. As for gen II, I can't think of a single Pokemon I dislike.