I recently purchased a Pioneer VSX-84TXSi, but the dealer screwed up the order. Long story short, they lent me a Denon AVR-4306 until they can get the Pioneer in. I've now had the Denon for about 2 weeks. I haven't listened to the Yamaha 2700, I was looking at the V1700.
At the moment, the Denon is setup to drive my Def Tech Mythos one towers, Mythos 3 center, Mythos Gems for surround and Def Tech Supercube 2 (powered sub).
Strictly from a sound quality standpoint, I have no complaints at all with the Denon. The 130w are plenty of power and I think I only went over 0db once so far, and even then it was really for testing and not because I want to listen to music that loud. However, I can tell you that I found the Denon to be cleaner than the Yamaha in my samplings when I tested the V1700 against the Denon 2807. The Yamaha seemed to clip a little on some of the more demanding movie sounds and it was noticable in the sub.
From a usability standpoint, the Denon is not the easiest AVR to setup. And I have still yet to figure out how to connect it to my MP3 player or my external 160GB HDD loaded with music. I also couldn't get the auto room eq to work because you have to connect it to an external display just to see the setup options. But if you spend a little time with the owner's manual, and you have your TV connected to it, you should be okay.
From a features standpoint, the Denon seems to be able to do pretty much everything the Pioneer can do. They both support 3 zones, which I specifically need, and they both have 7.1 support. Connectivity is pretty even too, except the Pioneer has 4 vs 3 HDMI inputs. Although the Pioneer has 140w vs 130w, I don't expect to hear the difference. The Pioneer has THX certification, which doesn't mean much of anything. The Pioneer also throws in the iPod dock, whereas Denon charges an extra $60.
From my perspective, the Denon is a great receiver, but overpriced. At $2000 msrp, it is $500 more than the Pioneer's $1500 msrp, but it doesn't seem to offer anything for that extra $500. In fact, the Pioneer seems to have a couple of minor advantages. Comparing prices with the Yamaha, it appears to me the Yamaha is also cheaper than the Denon, so the big question for me would be, what does the Denon do that warrants the extra cash? Either way, I would think any of these 3 receivers are an awesome piece of equipment for any HT setup. I don't think you can go wrong with any of them.
But in the end, it's your ears and your wallet that makes the final decision. So take your time, check them out, and maybe even bring one or both home as a loaner so you can take your time playing with it and testing it in your home. It's pretty hard to be test them thoroughly in the store, so ask if they have a money back satisfaction guarantee - I know Magnolia does it.