Dungeons and Dragons, easily. I've been flailing at it since I was ten. Full-steam ahead all through high school. Several games in college, though it was rarely the 'main' game. A four and half year game that bridged 3rd edition into 3.5, plus a pile of Living Campaign play at that same time, all of which kind of burned me out for awhile. A bit of 4e, and now online Adventurer's League with 5e, and some games with the kids.
At a guess, probably four or five hundred sessions of DnD, over the years. It may not be my all-time favorite game, but… I mean, numbers don't lie.