Neither are truly cutting edge fantastic, as there are many drumemrs form Mike Portnoy (Dream Thater) to Daniel Erlandson (Arch Enemy) to Morgan Rose (Sevendust) who are many times better.
But both are very good and fit well into the sound fo their respective bands. And as it happens, both are a tad on the jerk side. But realistically most people who call Lars an jerk do it because it is the "Cool" thing to do, and over the Napster thing (ancient history, and excuse me for not crucifying a guy for not liking having people steal his stuff. Just because the modern generation seems to think Pirating is ok doesn't make it so)
But simply because, Lars does play a faster rtempo, and was one of the pioneer of machine gun double kick drums, I have to give it to Lars. I listen to both, and know Lars could certainnly play any Motley Crue drumline, but I cannot say I feel as certain about Tommy being able to replicate all of Metallica's.
23 years of listening to both bands, and having met the members of both bands. Lars is a tad uptight, but from what I saw he was no bigger a jerk than most of the people on here that bash him.