Another one, huh? I suppose I can give some quick overviews! :P
A weasel that has pretty good Speed, but that's basically it. Until it evolves into Floatzel, Buizel is a pain to train, having below average Defense, and terrible HP. Once it evolves though, it's very fast, and has good very good Attack and Special Attack. If you don't mind a crappy Pokemon at first, then Buizel will be your best friend!
Covered him in the last question.
An odd choice for a Water-type. Can be caught near the hotels via a good Rod. It has very low Defenses its whole life, but has a very large movepool, and good attacking stats to back it up. Once it evolves, it'll have very low Speed, better Attack and Special Attack, and somewhat better HP. They're also fairly easy to train, Experience-wise. Recommended for beginners.
An even odder choice, and is not (AT ALL) advised. With rounded stats, it sounds promising, but rounded stats means nothing if they all suck. It has an oddly useful addition of Gust, and naturally learned Rain Dance to help it, but unless this playthrough is a complete JOKE, I wouldn't even consider Finneon.
Gyarados. Nuff' said.
Evolves into an average sweeper, but the horned appearance makes for some cool Move Tutor attacks. Just your average sweeper with High Attack and Speed. Nothing really stands out about Goldeen.
A fair choice. Psyduck evolves into Golduck, who has access to some cool attacks, like Zen Headbutt, Psych Up, Signal Beam (Via Move Tutor), and more! His stats are fairly average, but that's all made a little better with different types of attacks.
A Special Wall with high HP and Special Defense. Once it evolves, it gets MORE HP and Special Defense, but gains an acceptable amount of Speed and Special Attack as well. A very versatile choice with a pretty useful typing.
A very useful typing, and makes a great tank. With flaringly high Special Attack and HP, and acceptable stats everywhere else (except Speed), Shellos makes a nice addition to any team. Also recommended for Beginners.
I'm almost positive that all of these can learn Surf and Waterfall (Well, Wingull will, when it evolves xD), so take your pick! I'll mark out the Routes again:
"VERY EASY" ROUTE: Shellos / Psyduck
"EASY" Route: Buizel
"INTERMEDIATE" ROUTE: Remoraid / Goldeen / Wingull / Tentacool
"HARD" ROUTE: Magikarp (Could be Intermediate, in some situations)
"VERY HARD" ROUTE: Finneon