Pikachu
Pikachus have lower health and stamina, however their speed makes them harder to catch.
Eevee
Eevees are fast which makes up for their lack in strength and health.
Mewtwo
Mewtwos have a very high strengh and stamina. This means there opponents need to be cunning.
Charmander
Charmanders are very cunning and dangerous creatures. You better get ready for a knife fight.