I always choose Torchic, 2nd choice would be Treecko. Mudkip kinda.. you know.. sucks.
It's EV's aren't bad, but water types are plain useless. I guess grass types are too, but they're pretty fun. In FRLG I always got Charmander, even though I preferred Blastoise. Fire types are the most useful throughout the game, though I always tend to drop my starter sometime after the 3rd gym.