Federer is by far the best volleyer on tour. His doubles record backs this up. To be able to beat the Bryan Brothers at the only game they know, is unheard of with a random doubles pairing. Fed came into net on almost every point where he had the chance, and he won almost all the time.
Federer is a very good volleyer, no doubt. But the best? Not for me. Most doubles specialists have better volleys: Bryan brother's, Leander Paes,.. He could be the best and probably would be given his talent if he practiced it as much as those doubles specialists, but he doesn't.
Singles players are better players than doubles players. They have better serves and returns. So if you put a "random doubles pairing" together and they have enough incentive to win they can do very well. The main advantage that doubles specialists have, is that they have mastered the tactical side.
In 2004 Malisse and Rochus got together in RG. They played a lot of doubles at the juniors, but that was about it. They got eliminated in singles at some points so they shifted their focus to doubles. They won it, beating doubles specialists pairing like Bjorkman/Woodbrigde, Bhupathi/Mirnyi and Llodra/Santoro.
Take the 2004 olympics as well. Olympics are a good example because they will be motivated to do well in doubles. Lots of high single ranked players who made a team in doubles did very well. Gonzalez/Massu defeated Bryan/Bryan, Ancic/Ljubicic defeated Llodra/Santoro and Kiefer/Schuettler defeated Bhupati/Paes.
Dick Norman is an interesting case as well. 38 years old or something and for years he struggled to make it in the top 100. He even retired at some point. But much to his surprice Wesley Moodie asked him to form a doubles pairing. He decided to make a comeback in doubles at has now reached the final in RG and the semi-final in Wimbledon this year. He was an average singles players who with the guidance of an experienced doubles players very quickly became top in doubles.
Now do all these players have out of this world volleys? No. Some have very good volleys like Kiefer, Ancics,.. but I don't believe there lies the difference. Federer has very good volleys, but to say he is the best volleyer on tour because he beat Bryan/Bryan with another top 10 player is pushing it a bit in my opinion.