Huh, I found (after playing and beating both versions) that B.O.B. was actually quite a bit better on the SNES. I played the Genesis cart first, and the SNES felt like a real upgrade. I wrote up a comparison here:
http://www.sega-16.com/forum/showthr...l=1#post511733
The 30Hz scrolling and lack of a dedicated punch button really hurts the Genesis version. I also found that it was a lot easier to spot dangerous (i.e. damage-causing) sections of floor in the SNES version.
This topic is one of great interest to me, especially when it comes to less-popular games (since most of the more popular ones have been done to death).
It might seem like a dubious honor, but I find that cross-platform shovelware is often a real win for the Genesis. It may not look or sound quite as good -- gradients/dithering, poor implementation of FM synthesis, etc. -- but those games often have a lot more slowdown on the SNES, and the Genesis's higher onscreen resolution often gives you a larger playfield.
One example is the Itchy & Scratchy Game. Far too often, in the SNES version, you literally can't see Scratchy coming because you lose those horizontal pixels that make him visible in the Genesis port. Even though the Genesis game is only a prototype, it's significantly more playable than the officially-released SNES game.
Or take the Chester Cheetah games, especially the second one. ("I'd rather not," everyone replies.) The slowdown in the SNES port is absolutely nuts -- it starts to chug with almost nothing onscreen.