in terms of pure hours, probably WoW yet... between beta and the first two expansions, think my /played was around 130 days or 3000 hours. put about 50 days into beta and think 60-70 into vanilla and TBC. WLK was maybe 10-20.
for non-online games, gotta be FF Tactics and GTA 5 now...
FFT at 13 full playthroughs IIRC (got them all on an old memory card or then one on a PSP and another on a PS TV). usually 50-100 hours each and a few higher than that. must be over 1000 hours for sure tho.
GTA5 up there, certainly for being a 2013 game. excluding GTA Online (another 750 hours), I think I put around 700-800 hours into it across 2 main files and maybe 3 quick playthroughs over 2 gens.
Deus Ex, Shadowrun (Sega Genesis), FF Tactics and Tactics Ogre, WarCraft 2 and 3, and Age of Empires and Mythology though are all up there in terms of non-hours which games I've most consistently replayed every single year over and over. For pure hours tho FFT is way up there, though, even of Tactics Ogre -- a game I like more. It's just FFT is streamlimed in a way it makes it so easy to replay every year.