Staryu/Starmie are generally better Pokemon, due to their Special Attack, Speed, and Type Coverage over the Slowpoke chain. If you want a bulkierPokemon, go Slowpoke.
Starmie @ Leftovers
Ability: Natural Cure
EV Spread: 252 SpAtk, 252 Spd, 4 HP
Hydro Pump (Move Relearner)
Recover (Move Relearner)
Ice Beam (TM)
This moveset is good for in-game, as it gives you nice STAB, coverage for Grass with Ice Beam, and Recover for some health restore.