CoD easily...
I have like 800 hours on CoD4 alone. WaW was like 200 hours until i swapped it. This + all the other CoD games ive played either online or off... EASILY above 1500 hours worth of gaming.
Second place would have to go to Final Fantasy, about 3 playthroughs of FF7... one what went over 100 hours + 2 others around 60-80 hours each.
FF6 had one playthrough as did 9,10 + 10-2.