As a general rule, the Genesis was better at fast-paced arcade and sports games. EA Sports, Sonic, Gunstar Heroes, Herzog Zwei. That sort of thing. The Super NES was much better with RPG's and the slower-paced adventure games -- think Super Metroid, Mario, Zelda, everything by Square.

Of course, Genesis had Phantasy Star 2 & 4, and the SNES had Contra 3 and Castlevania 4. But those are typically the exceptions.

I remember that the SNES Mortal Kombat 2 was by far the better version (the best home version on any console), and Pac-Man 2 also looked and sounded much better on Nintendo. SF2 was another common sight: the Genesis version had more animation, but the SNES had much better audio (no scratchy voices - ugh). A lot of third-party games followed that rule, too.