Best Integrated, period.

According to Ken Kessler in the July 2013 Hi-Fi News, a new contender for the title is the Krell S-550i, if very high power into difficult loads *and* good sound are the criteria. It can drive Apogee Scintillas with 2400 stable watts into 1 Ohm, and regarding sound Kessler didn't miss the ARC Reference 75 or his old Class-A Krell.

I tend to agree with Donjr (Simaudio Moon, D'Agostino, Merrill Veritas, Bully Sound, etc.), but it's difficult to shy away from tube *preamps* like the Audio Research Reference 5 SE, Purity Audio, or Herron.