3d is a gimmick you will use about 3 times and then decide it is overall tedious. It isn't worth it for games and only some movies work properly with it.
120 Mhz though is already a nice refresh rate and will vastly improve your experience.
144Hz is the ultimate solution, only bested by G-sync for Nvidia or Freesync for AMD.
If you have the budget, look into those two technologies, depending on your hardware. If it is between these two, I recommend the 144Hz screen. You won't believe the smoothness.
Can you please post ur specs, for better advice from us?