To the best of my knowledge, nothing beauts Arctic Silver 5. If you are working on a system that you don't want to risk using metallic base compounds, Ceramique from Arctic Silver is great stuff... Apparently they now have that in a version 2.
Personally, I even still have a tube of Arctice Alumina. If I was going to buy one for a bunch of techs to use and had to eat the liability, I would buy Ceramique 2 because you would have to be an idiot to mess anything up with that... it could probably overflow onto the socket without causing problems (though I wouldn't want to try it).