I've never played BSD so I can't comment on that, but WH2O is a fun game with lots to do. I seem to be in the minority here, but the theme wore on me after awhile and I couldn't stand hearing another round of that music either. The whole strategy of hitting the skill shot, hitting the whirlpool, catching the ball, flipping it back to no way out, hit insanity falls, then repeat got a little boring for me. Then again, if my shooting is off, the game kicks my ass, lol. It throws modes in there to break that cycle up, but it always comes back to that simple strategy. But, if you've never owned one, you should definitely get one some time.
I would buy whatever you can get the best deal on at the time and don't over pay for a game because it is hyped up.