He's definitely up there...that's not even counting his kickboxing career where he fought guys like Hoost, Sefo, Le Banner, etc.
BJ Penn has to be the guy that had the hardest strength of schedule in terms of having the fewest "give me" fights.
-His first MMA fight was in the UFC and he fought the best lightweights they had to offer.
-Fights Gomi and Hughes when they are the best lightweight and welterweight in the world
-Moves up to middleweight/light heavyweight to fight the Gracies and Lyoto Machida
-Comes back to the UFC and fights GSP and Matt Hughes at welterweight
-Wins UFC Lightweight Title, holds it for 2 years
-Fights Frankie Edgar twice
-Moves back up to welterweight and fights Jon Fitch, Nick Diaz, and Rory Macdonald
His last few of fights were against Frankie Edgar again and Yair Rodriguez, two top 10 featherweights.
No easy fights in Penn's career..