Too hard to call I think.
I mean time-wise I probably spent more time playing Street Fighter II and various iterations since then any other game, but best game ever? Probably not.
I also love Super Mario World and Mario 64, not so much on Sunshine just felt it was missing something and Ocarina of Time is of course awesome.
I have a few personal favourites such as Escape From The Planet of The Robot Monsters on arcade, Meglomania on Megadrive, Chrono Trigger on the SNES and Final Fantasy VII.
Whilst dated now, Halo is truly genre defining imho. Not many games I have sat for hours throwing granades under a truck to see what will happen - loads of fun!!