Lombardo by far. He was solid enough on the classic Metallica albums, but Ulrich couldn't even dream of rocking an album the way Lobardo carried South of Heaven, or Reign in Blood for that matter. I'm not a drummer, though, so I could be missing something about Ulrich, but he always seemed merely good--very energetic and enthusiastic--but very limited in his technique and ideas. And maybe I'm being negatively influenced by his douchebag personality.