I'd have to say Froakie. The year before last there was a lot of arguments about his evo's but no matter what I still thought he was awesome. Mudkip and Totodile are 2nd.
I like a ton of the starter Pokemon. But when it really comes down to it, my top favorites are Charmander, Turtwig, Treecko, Oshawott, Cyndaquil, and Froakie. Mainly because of their final forms, though.