The one I've run the most often is X1, "The Isle of Dread." I think I've run this module for every gaming group I've DM'd since the 1980s. I've run it as-written about a half dozen times, but I've also reskinned it to be a plane crash survival adventure for D20 Modern, a Call of Cthulhu mystery adventure, and a Norse-themed seafaring adventure. It's easily my favorite.
Others that I've run more than twice: X4, "Master of the Desert Nomads" (and its sequel X5, "Temple of Death"), CM1 "Test of the Warlords," and X11, "Saga of the Shadow Lord." The entire BECM line of modules are the best D&D adventures ever written, in my opinion, but these are at the top of the heap.