Chikorita - cute green pea. More of a supporter than beater but can pull its weight when needed. The "bad" matchups are either patheticaly weak, can be neutered with Geodude or have secondary grass weakness. Also surprisingly it's most viable starter in Gen 2 competetive lul.
Totodile - My childhood favorite, but now i'm kinda eh with it. it's still most broken of the three in-game. Ice coverage right when you hit Goldenrod, evolve at level freking 30, mono-water is good typing...
Cyndaquil - probably my least favorite of the three, but i still respect it. Fire + normal moves, with lol Dig and Rollout up to level 38 which is pretty late in the game. Still, after that there's only few things that can live thru Fire + Electric coverage.