The way I see it, him and Anderson are both their division's GOAT's, and have beat the 2 and 3 guys in their division(Nog and Cro Cop, Hendo and Rich)
Fedor did his best work in PRIDE, when it was on top and the premier Heavyweight division, Anderson's doing his best work in the UFC, where the middleweight division is premier.
You can make the argument Fedor fought smaller guys and won, you can make the argument Anderson went up in weight and destroyed a former champion.
Every fighter has fought cans, every fighter has some good victories, they both have a few losses. I'd say Anderson is, just based on the things he's able to do, the destruction of Forrest, front kicking Vitor, the comeback against Chael. Anderson is just a special kind of fighter.