Great question.
Funny that they are both "DE" but play very different positions.
The percentages and what not on this thread are great, and the opinions by those numbers are logical and "good stuff boys, good stuff"
Comparing the two WITHOUT money (yes, I understand that was the original question) they are both elite athletes for their size.
Mario Williams is a freak of nature. Charlie Casserly knew what he was doing when he drafted him 1st overall. 300lbs men who are as athletic as any LB'er, TE, or even some RB's are very very rare.
That takes us to Calais Campbell. I would say to Williams atheleticism, speed, and quickness, Campbell isn't at Williams level. But, when you talk about intensity, and POWER Campbell is better than Williams. And the SCARIEST thing about Calais Campbell, is I agree with Darnell Dockett in Campbell could easily put another 10lbs on without effecting his speed. Campbell is just a freak, and the more his mind catches up with his body, the closer he will be to being, IMO, the best 3-4 DE in the league. Gotta keep Campbell in AZ long term.