I have to agree with bbjd7 here. As good as Fedor is, he isn't a knockout artist. AA is the most athletic HW in MMA and his hands are definatley better than Fedor's. Fedor mauled Herring mainly from the gaurd and side control, not really standing.
But yeah, nobody is better at punching from the gaurd than Fedor.
Well, in fairness, I haven't seen Fedor attempt to finish many (if any) fights on his feet. I agree that he's not a knockout artist, but I've seen him throw leather as fast as any fighter I've ever seen. He's not as precise as Arlovski (precision has a lot to do with being a KO artist IMO), but I wouldn't say he isn't as fast or as powerful.
AA also depends on his stand-up alot more, where as Fedor tends to rely more on his Sambo background. So I would say that AA is the more refined striker of the two, and judging from body types alone, one would say he is more athletic. But I wouldn't put my money on Arlovski in a fight against Fedor or Barnett.
This is just my opinion, of course.