60 to 120 or 144 is a big difference,
120 to 144 isn't huge.
FPS games tend to benefit the most, but I noticed a huge difference in how fluid games are going from a 60Hz panel to a 144Hz panel in FFXIV (A MMORPG like GW2), even though I can only get 90FPS in FFXIV its a heck of a lot smoother than the 60FPS I had prior.