I have 441 hours in Town of Salem (Steam). I'd say I probably spent more time playing console titles though; easily multiple thousands on older renditions of Phantasy Star Online, Battlefield: Bad Company, and the like. Not to mention mobile games and stuff like League of Legends which are again, probably in the multi-thousand realm.
I think Dark Souls holds my #1 spot. Between playing it on the 360, PS3, Steam and PS4, I've logged well over 5,000 hours into the game.
I've also logged around 5,000 hours into Skyrim. I regret each and every single second of those hours.
Other games I've logged a large amount of time into would be...
Star Ocean: Till the End of Time (1,000-1,500 hours)
Final Fantasy Tactics (1,500-2,000 hours)
Dragon's Dogma: Dark Arisen (500+ hours)
Monster Hunter World (400-ish hours -- though this is mainly due to grinding for platinum)
Star Ocean: The Last Hope -International- (600+ hours -- again, mainly due to grinding out the platinum)
Toukiden Kiwami (around 400 hours, yet again thanks to a grindy platinum)
And there are other games that I've logged at least 200 hours into, but sitting here trying to recall all of them would take a lot of time, and I think this covers most of the big ones (close to or over 500 hours).