I'm gonna list the ones I like enough. They may not be super duper favorites, but it keeps my list from being more than Nidorina and Vulpix.
Favorites from Gen I:
Bulbasaur, Charmander, Squirtle, Caterpie, Butterfree, Rattata, Raticate, Pidgey, Numbers 29-33, Vulpix, Paras, Parasect, Growlithe, Psyduck, Abra, Bellsprout, Tentacool, Tentacruel, Magnemite, Haunter, Onix, Cubone, Kangashkan, Horsea, Porygon, Articuno, Numbers 147-149, Mew
Least favorite: None. I personalized all of them on some level way back when, so I'm sympathetic to each of them in varying degrees.
Favorites from Gen II:
Chikorita, Totodile, Sentret, Mareep, Flaaffy, Wobbuffet, Hitmontop, Miltank, probably some others I'm just not remembering
Least favorite: While I don't dislike any of the rest for any serious reason, I do think they're all kind of boring. Also, personalized everyone here too, but it didn't stop them from being dull.