Hard to really judge this. You can vary in skills levels at different things:
1. Soloing
2. Grouping
3. Raiding
4. Sheer knowledge of mechanics/game
5. PVP
I always thought this was the most interesting stuff in the game though:
http://www.project1999.com/forums/sh...tist+challenge
I think Mauricewhite, Svenn, and Save have impressed me the most when I've watched them play.