I would go with the Denon. Better receiver, sounds cleaner than the Yamaha, and I tend to hear a little more detail through a Denon receiver, especially with Jamo and Energy speakers. Having said that I have a Yamaha RX-A720 receiver hooked up to two CF-30 Energy towers and a CC-10 center channel. It sounds good, but I hear less detail and my center channel doesn't get the power that it craves with the Yamaha. I'm now actually looking to replace it with the Denon AVR-X4000, because of that issue.
Also what will you be doing mostly? Movies, Music, Sports?