In their respective primes?
Very hard to say, but 2 things to remember:
1. Fedor had incredibly fast hands
2. Fedor had excellent subs off his back (something DC lacks)
DC has superb striking for a wrestler, esp considering his reach. He has great dirty boxing, works uppercuts from the half-clinch, and has fast 1-2 combinations. And DCs TD game and top control is incredible.
Fedor is his prime had unreal speed and power with his casting punches, and casting protects the chin with the shoulder. Totally different style of striking from DC. Fedor also had terrific throws and deadly GnP and subs from top position.
People claiming DC would maul Fedor aren't remembering how ridiculous Fedor was in his prime.