I can't say what is "best", but I have been very happy driving my 3.6Rs with a pair of Aragon Palladium monos. These amps have lots of current, beefy power supplies (although I have been told newer ones have lesser PS).
That being said, Magnepans are very room dependent. I have been focusing a lot of energy into getting the room right for these magical speakers. Many HQ amps will drive these speakers well, provided the room is set up for them, and the AC going to the amps is as good as you can get it.
Room and electrical issues are as big a component as amp choice. Once those are addressed, the speakers are capable of producing world class playback.
