Considering I just finished replaying Crystal, I'm gonna reserve
Poliwag and
Tauros, the other Pokemon I used in addition to Chikorita and Abra.
But this leaves me with a question. Will you take separate entries for Pokemon different between games? Examples including Poliwag and Growlithe being available much earlier in Crystal.
Poliwag for High/Mid tier
-Availability: Very Early in Crystal, Early in GS
-Stats: Fast, fairly strong and bulky once evolved
-Moves: Decent. Surf + Ice Punch is about all it needs
-Power: Fairly strong, gets some powerful moves early. Requires a bit of grinding to get past the "Bubble stage", but still useful.
-Type: Water-types are always useful
-Match-ups: Doesn't excel against any boss in particular (except Brock and Blaine in Kanto), but doesn't really lose to anything.
Tauros for Mid tier
-Availability: Mid-game
-Stats: Fast, with high Attack backed by decent bulk
-Moves: limited to Normal moves and Iron Tail (and later, Earthquake)
-Power: Quite strong, Strength/Headbutt can bust through most things that aren't Rock- or Steel-types. Once it finally gets Earthquake, good luck stopping it
-Type: Fighting-types are not particularly common in-game, so it's good typing
-Match-ups: can't touch Morty or Jasmine, loses to Chuck, and doesn't excel against anyone in particular. Not the most useful, but still not bad