Man I don't know that's a hard decision, but I would have to say that I was never more excited than when I first watched the Hughes vs. Gracie fight. That was probably one of the best match-ups ever and just exciting thinking about Royce Gracie getting back in the Octagon. I was a bit disappointed at how quickly it was over but it was awesome. I never bought the UFC events on PPV until UFC54 I think so I can't say Liddel vs. Coutoure II like most others will but I remember Liddel vs Coutoure III was pretty exciting. It's too hard for me to say which was the best, cuz really they all have at least one good fight and at least one bad fight. Plus I get most of the undercard bouts mixed up to which UFC it was.
UFC60 would prolly be my top pick. I think it was probably the biggest and most important fight in UFC history.