I really don't like any of the water starters. The only first form that I like is Mudkip, but I also think that Totodile is okay.
My favorite part about the water type starters (and most other starters, really) is the middle evolution. Marshtomp is one of my favorite Pokémon and I am also fond of Wartortle. However, Prinplup and Croconaw were a bit too rough.
My most disliked part about all Water-type starter Pokémon is the uglyness of the final, fully evolved forms. Prinplup and Croconaw were too rough and "boyish" from the get-go, and their final forms didn't help much to weigh out that argument. My most favorite one out of these would probaly be Swampert, although I don't really like it either. Blastoise was a bit too simple and the ugliest out of the four IMO.
So, that's my opinion on the Water-type Starters~