It depends on the game and hardware used. It wouldn't be wrong to assume that nvidia performs better than iz3d but i don't think the difference is big. Tridef however takes quite a hit (remember i have an ancient machine) performancewise but it has hands down the best visual quality (least ingame anomalies) of the 3. One thing to take into account is that iz3d doesn't seem to be updated anymore even if the software still plays decent with several games.
Mb: Asus P5W DH Deluxe
Cpu: C2D E6600
Gb: Nvidia 7900GT + 8800GTX
3D:100" passive projector polarized setup + 22" IZ3D