Water types, agreeing with many other people up there. X3 Next would be Electric, Grass, and Normal (has the best variety).
Water Team: Politoed, Milotic, Corsola, Swanna, Azurill, Vaporeon
Electric: Ampharos, Raichu, Emolga, Manectric, Zebstrika, Pachirisu
Grass: Lilligant, Whimsicott, Bellossom, Leafeon, Meganium, Tropius
Normal: Delcatty, Eevee, Jigglypuff, Spinda, Chansey, Cleffa