If we're talking about 2000 to 2010, you've got to remember that this covers 10 years.
Some riders who are considered the best these days didn't start riding untill half way though the decade.
20" for me is CLS, his riding has been more influential than anything / anyone and opened up a whole new type of trials riding. Brought out amazing vids etc.
24" must undoubtedly be DannyMc.
26" TRA, he's been going strong for nearly 10 years now. NT and Damon maybe too?