I got better low end PEQ results from the Audyssey, below around 100hz, than with MRC. That being said, I didn't like what Audyssey did in higher frequencies and wouldn't use it outside the subwoofer channel. This is in a pretty well treated room.

Above 100hz or so neither the Audyssey nor MRC really nails my room.

User interface on MRC, and repeatability, both are pretty poor.

DirecTV HR21, Ram modded Oppo 93, JRiver MC17 on Win7 wi/SSD, Empirical Audio Ultraclock Offramp, 861v6, Bryston 28B SST2 amps, Salk 12" Soundscapes with Dueland caps, RAM modded Audyssey Balanced Pro, Lumagen Radiance, MarantzS4