I typically stick with the water-based starter. When I first played Pokemon, me and my brother argued for hours over who would get who (we didn't want the same starter, since we planned on helping each other complete the Pokedex). He won for Charmander, me Squirtle, so ever since then I've been the water starter.
Of the five gens though... I think Oshawott has been my favorite so far (Gen V).