I can't really choose one game over another if I like each one so much... they're all special in their own ways *opens drawer with games in it* *gives games a nice lil' pat*
buuuut I'll just list some very likely ones...
FF7/10... Chrono Trigger... Zelda: LttP... GTA3, and MGS...
the end *runs away*
But if ya wanna judge by hours (like justin said) it would be either GTA3 or FF7... actually, maybe Chrono Trigger instead of GTA3 because I've beaten Chrono Trigger like 2 times and started playing it again a third... but I'm not sure...
I've played the hell outta GTA3... And I beat FF7 twice (and the first time took me 70 hours)...