I'd say Skyrim on Warframe. The amount of hours I played Skyrim on X360 and PC add up to about 400-500 hours. As for Warframe, I've invested about 300+ hours into that game.
I've 100% Dragon Warrior Monsters and speedrunned it an uncountable number of times, so it is probably that. If that wouldn't count; maybe Monster Hunter 4 Ultimate or Touhou.
Got 950 hours in Terraria (some afk hours there, but still a lot nonetheless) I've also gotten 186 hours in Binding of Isaac: Rebirth (which'll probably increase drastically when Afterbirth comes out) Pokemon games combined are probably in the thousands o_o Also spent a good while on osu, I've taken some long breaks here and there but when I didn't I usually played for a couple hours per day.
Currently its League of Legends with about 600 (A game i don't even play anymore) followed closely by cs go at around 550 (A game I play rarely nowadays) Next would probably be osu followed by something like TF2 or Dota 2 which somehow I have a hundred hours in both without ever remembering playing them.
Ultima Online Over 7 years if active playing everyday, as of now I am pretty much inactive but still play once in a while
Romance of the Three Kingdoms II Close second place. Played it over and over and over and over again, still do play sometimes today. Done so since the mid 90's. I played enough that I know the force and weakness of every generals in the game. When I want to play nowadays I need to take all the rulers, and mess up the start of the game massively, otherwise I can predict everything that's gonna happen and kills some fun out of it. But I still somehow like to play it, call it nostalgia I guess.
disgea 1,2,4, Final fantasy 4,5,6,7,8,12 growlancer 2 and 3 hell all of the RPG games i own yo! oh yea all Gran Turismo and tokyo extream racer games too. i still got a lot of games that i need too finsh but not a enough time!
hey yo! just to let know if you see me posting here there's a 70% chance that I'm drinking some cheap alcohol or 10% chance that I'm posting here while drinking the good stuff heeeyea!!!!. 10% chance I'm might actually be too drunk to post trust me you'll know when that happens...... or maybe just maybe you might see me sober here lol