My company is direct authorized dealers for Denon, Pioneer, Pioneer Elite, Onkyo and Yamaha so from a business point of view I have no preference.
Regarding the rated power vs. the actual power output issue, Pioneer tells me that's simply not true. From what I was told they build a very electrically efficient power amps, video-processors and power supplies that can deliver very high peak power when the demand is called for. Not sure what the truth is, but I can 100% assure you that the VSX-820-K can drive high end tower speakers at reference volume levels with no trouble and no noticeable distortion.
Personally I have several Denon, Pioneer and Onkyo receivers in my home systems. My basement theater has Denon's AVR-4810 driving a high-end 9.4 speaker system. My living room has Onkyo's SR875 and the master bed room has Pioneer's SC-25. They all perform very well and each has their strengths and weaknesses.
-Robert