tricky I really dont know but probably:-
1/2*)FFVII completed it over 10 times now each varying lengths in times taken but I would say ive probably spent over 500 hours on this game and I still play it.
1/2*)Street Fighter 2 (all versions but hyper the most) honestly not sure if this would be 1st or second I played it for years and years so I dont know but I wouldnt be surprised if I have played it for over 500 hours I dont play it so much now because no one will play me
3)WOW I dont really play it but I racked up just under 3 weeks play time over all which is a pathetic amount compared to some people but is still quite a bit and its just under my time spent with FFVII (est) so in fact all these games are pretty close.
Actually mario all stars would be up in there as well if I cheated and classed it as one game it may even be the one I have played the most.