If MMOs, Runescape with a bit over 300 days , or about 7200 hours. If no MMOs, about 400-500 hours into pokemon emerald.

Pokemon Y for over 350 hours

The longest story I've played was Xenoblade. Around 80 hours. The longest I've spent on a game was probably Pokemon Blue. Hundreds if not thousands of hours spent on that.

Pokemon Diamond, that was just crazy how much I played that. If we dont count Pokemon games though it would be FF12 at 120+ hours

I wouldnt know. I know i have put more time into chrono trigger than any other RPG game.

Final Fantasy X => 221 hours (done almost everything and maxed out all characters)

Probably Pokemon Gold with somewhere between 200-250 hours which I used to think was a lot until I saw some of everyone's post about Pokemon hours played lol

If MMOs count: WoW, I think I have a playtime of around 2 years on this, but around half of the time was idling in one of the cities while I did something else in RL (quit 2 years ago, so can't check)
If multiple "playthroughs" count: Gothic II, played that for >200 hours
Single "playthrough": Hard to tell but I think FFX, played that for ~70 hours I guess (including the dark aeons, monster arena etc.)
If only the time until I beat the final story boss for the first time counts: I'm again not sure, could be Ni No Kuni (~40 hours), but I don't really remember how long I needed for games like Gothic 2, Guardians Crusade, Golden Sun, older FF games among others

Defenatelly Pokemon Leaf Grean.I remember that I've finished this game at least 5 times with at least 100-200 hours put into each playthrough.But except for pokemon.....I've played Dark Souls more than 250-300 hours.Also I've finished Kingdom Hearts 1 five times plus a lot of unfinished playthroughs.

Precisely 100 hours on New Vegas + all DLCs on Steam.