Even though probably 95% of the games I've ever played were on consoles, the ones I've sunk the most time into, by far, are on the PC. The one I've spent the most time with is not really a game, but a MUD (sort of like WoW, except text-based and free). I spent a ludicrous amount of time playing it which I'm not going to reveal, because it's scary.
As for actual games, I've probably put no less than 2000 hours into Heroes of Might and Magic I-IV and their expansions and tons of player-made maps, with III taking probably 80% of the time there. Also, I've played each of Might and Magic VI-VIII multiple times, probably racking up hundreds of hours there.
Consoles - I've never been too OCD about getting perfect games and whatnot, so on a single playthrough I don't think I've ever gone above 100 hrs on any game. Combined playthroughs probably put Xenogears at the top of the list, with FFT somewhere closeby.