I've never actually owned Black or White myself, though I reckon there's not much difference in Black 2 and White 2 when it comes to starters. In any case, I have played a bit of BW through downloading a ROM of it (I know :( ), in which playthrough I picked Snivy, since I found it to be the coolest of the 3. I never really played too much of BW though, since I generally don't like to play ROMs, since it for some reason just feels completely different. In any case, I actually really liked using Snivy, but its third stage never really appealed to me, which was what kept me from picking it in BW2. Well, that and the fact that I'd already used it :p
In BW2 I picked a Tepig and named it Pokabu (because I like that name so much more ;D), and I actually don't really know why I picked that one instead of Oshawott. I think it might've been coupled with the fact that I didn't really like the Oshawott line too much either. To my surprise though, I actually came to like it a lot, and it definitely became a valuable part of my team, and I kept throughout the entire game. I honestly think it's one of the starters that left a bigger impact on me, since I honestly hadn't expected much from it, and it turned out to be really great, whereas I usually pick starters because I already know that they're great. So yeah, that was fun :D
Guess I still have to try out Oshawott eventually, but that time will come! I did get one off the GTS, with Pokérus even! Though it's not quite the same when it isn't your starting partner, so I never really used it.