Toughest matchups for Federer, in order
1. Nadal. No explanation necessary.
2. Berdych. Emphasis on this being in the present. I'm sure this will be hotly contested, but I contend that Federer has a better chance of beating Djokovic/Murray at this point than he does Berdych.
3. Murray. Murray has a level that, if he plays to it, Federer can't match at this point.
4. Djokovic. Federer/Djokovic matches, even now, basically come down to a coin flip. If Federer comes out on fire, he can beat Djokovic anywhere but possibly at the AO. If Federer is lackluster, Djokovic will take him out.
5. Del Potro. I give him the edge over Tsonga as he's been tougher, more consistently. His backhand isn't something Federer can attack in the clutch moments, unlike with Tsonga.
6. Tsonga. Federer generally finds a way to handle him, but the serve and forehand power are still really dangerous to Federer.
7. Simon. They've only played 3 times, but this is not a guy Federer likes playing.
8. Benneteau. It's no longer just a fluke thing. He's beaten Federer twice and scared the crap out of him at Wimbledon.