I think either the Safin one, or the Wimbledon one. The Australian Open final just fizzled out so hard in the 5th, and the Nalbandian match he basically just tanked the third and fourth sets once down a break. The USO 11 semi would be close with the other two, but the fact that the underdog lost that one and won the others takes the excitement factor out of it a little bit for me.