The only reason I'm choosing Froakie as water types being chosen to me is a long standing tradition:
Red: Squirtle
Gold: Totodile
Emerald: Mudkip
Diamond: Piplup
Platinum: Piplup
SoulSilver: Totodile, Squirtle and Mudkip.
White: Oshawott
Black 2: Oshawott
White 2: ... Oshawott again maybe?
Y: Froakie