I have owned several Denon receivers, a Pioneer Elite, and a Marantz (SR-7008) and am currently on my second Yamaha and not looking back. Pioneer today is not the Pioneer of old, it is now a wholly owned subsidiary of Onkyo. As Onkyo has had and, based on current posts here and elsewhere, continues to have QC issues I would not buy a Pioneer myself. That notwithstanding, IMO Pioneer receivers are not quite as nice as D&M products and Yamaha products.
Their automatic room calibration (MCACC and MCACC Pro) lags behind both YPAO and Audyssey. As far as basic sound quality goes I doubt seriously anyone could tell the difference between any of these. In the end, I chose Yamaha Aventage based on superior build quality (all steel/aluminum construction) and what I perceive to be better reliability based on what I've gleaned here and on Reddit and home theater shack forums. I will say too that I like the styling of the Yamaha Aventage line as well.
Yamaha Aventage RX-A660
Martin Logan Motion 12 Mains
Martin Logan Motion 8 Center
Martin Logan Motion 2 Surrounds
SVS SB-1000 Subwoofer
Sony Bravia XBR-55X930D