I really can't say a specific game, but I'm sure its either a Final Fantasy or Pokemon game. I've spent at least 100+ hours per game in each series. xD;

This gen its Lost Odyssey played that over 130 hours currently on my second play through unfortunately its not a new game plus one since I lost my original save file. Last gen I don't know I started a lot of them but only finished a few. On the PS1 its Final Fantasy VII played that for hundreds of hours with Breath of Fire III a close second place played it for a little over 100 hours.

pokemon diamond, maxed at 999 hours, don't know exactly how much of my life was wasted playing it because the counter gave up.

Baldurs Gate II w/ Throne of Bhaal

Pokemon:Saphire over 500 hours

Runescape by far.

Without counting MMOs, Star Ocean: Till the End of Time. I have around 120+ hours on that game. I don't even know what the fuck I did to amount that much time.

I'm bad at keeping track of my playtimes. I like that the newer consoles do that for me. I'm over 350 hours in Monster Hunter 3 Ultimate, if you want to count that as an RPG. If not, I just hit 150 hours in Pokemon Y. That's probably going to get a bit higher over the next week.

Dragon Dogma Dark Arisen (275 hours) Char Lvl 175 - I really couldn't get off the game.
Dark Souls Prepare to Die Edition Char Lvl 100 (Over 100 hours.)
Demon Souls Over 50 hours (Stopped playing it after about 1 and a quarter playthrough.)
Elder Scrolls Skyrim 20 Hours - Stopped playing, it was crap - exploitative skills.

Currently playing Star Ocean The Last Hope (over 40+ hours so far.)

I'm quitting RPGs :)

Dragon Warrior 7. 75 hours, finished the game did most available side quests. Created every town except for the Casino town and got all the best equipment from each. When I stopped playing I didn't yet beat God or the other secret bosses.

Tactics Ogre Let Us Cling Together. 80 hours on a single route. PSX version. PSP version is garbage. I've beaten the game several times, on each route, but the longest I've played a single game and got all the secrets was 80 hours. Got Deneb, Ganb, and Randal, multiple angels with their highest possible stats by recruiting them during the Bishop Branta battle, got Radlum and finished all floors in Hell's Gate. Also got every single rare item that was possible to me in every battle, including those in Hell's Gate.

Nice I might go back and try to platium the game.  Still have to finish Valkyria Chronicles and my second playthrough of Lost Odyssey first.