With a lot of multiplatform games for both of these systems, there isn't one version that's universally better. Some aspects will be better, while other aspects will be worse. So it comes down to what you value more. For example, B.O.B. was originally developed for Genesis, so the music was created around that hardware and sounds like a mess on SNES. But they built an improved control scheme around the SNES controller, so the game plays better on SNES.