Pick a weight class (or you can just do it across the weight classes) then group the champs in one of 3 categories: Great, Good or Average. I'm not willing to say bad, cuz heck they were champs. But I am comparing them not to a category of UFC fighters, but compared to the other champs. Here is an example:
Great: GSP, Anderson, Liddell, Hughes, Aldo
Good: Franklin, Griffin, Sylvia
Average: Maurice, Serra, Cookie Monster
Great: GSP, Anderson, Liddell, Hughes, Aldo
Good: Franklin, Griffin, Sylvia
Average: Maurice, Serra, Cookie Monster