Who has (or had) the best conditioning and endurance in MMA? (but if you want to take it literally and discuss who owns the car with the best gas mileage, go for it. It's Christmas.) Nick Diaz? GSP? Prime Sean Sherk? Big Nog seemed to win fights in late rounds quite regularly. Randy Couture?
Edgar's is pretty good, people always say Cain has good cardio as well even though he hasn't been past the third round.
wrestlers tend to have the deepest gas tanks I think. GSP, Sonnen, Benson... honourable mention to Homonick.
DEEPEST, its hard to tell because some of them still go at 100% after 25 minutes so... guys like GSP, Bendo, Diaz' bros, Edgar, Condit simply dont get tired. Its hard to tell the one that could go the longest without showing signs of fatigue.
Edgar because he fights bigger opponents and got the shit kicked out of him in round one by Gray. It's harder to come back from that than GSP dominating Kos for five rounds or whatever.