I like both Pioneer and Denon and I do not think you can go far wrong with either choice. That being said, I think the Pioneer SC 65 is the better of the two (pretty much by far).
The Denon has MultiEQ XT, the Pioneer Auto MCACC Advanced. As has been said 100000 times, some prefer one over the other but IMO and in my experience MCACC is superior just because you can tweak it a lot after it makes the measurements. Yes, MCACC does not EQ the sub...big deal! You can tweak it yourself and I bet it will make your room shake when you do.
I have seen people say that, "Amplifiers in the same price range all sound the same." That is a load of garbage, I had a Pioneer Elite SC 57 and a Denon 2112CI and the Pioneer wiped the floor with the Denon, with or without the self calibration (my girlfriend, friends, and parents said the same as well). They both sounded awesome, but with 3 different speaker sets I had much better sound quality out of the Pioneer. Onkyo sounds nothing like Yamaha which sounds nothing like Pioneer and even Marantz sounds different than Denon (even though they share a lot of internals and they are made by the same company). Unless you have poor hearing, it is a very obvious difference. Ever receiver has a different sonic signature, they can sound similar but they are all unique. Then after you calibrate them using the auto-setup (MCACC, Audessey, YPAO, Tinnov, etc.) they will sound different even more.
The only thing about the Denon 3313CI is I bet it will be easier to setup for the average Joe (or Josephine). Pioneers are slightly more difficult to setup and operate but I think that is worth the strong points of the Pioneer vs the Denon. It should be noted that the 2012 Denon models are considered a step up/step back model because they added features while taking others away.
The Pioneer will sound better, have more power and headroom, look better, and has a 32 bit-DAC which should improve sound quality if you are using it for your PC sound or with other digital components. It has better video capability, and I do like Pioneer's MP3 restorer function better than Denon's as to me it just does a better job. The Pioneer also has a better video chip in it, and the Pioneer Elite's are sexy looking receivers.
I love both Denon and Pioneer, yet I think this is a no contest here. D3 Amplification + more power + Elite = winner Pioneer Elite SC-65.Denon highlights:
- Easier to operate
- Good all around receiver with nice features
- Excellent sound quality
- Audessey XT which some prefer
- D3 Amplification (runs cool and more advanced than A/B amps used in other receivers)
- Better (but more revealing) sound quality
- More headroom (louder at any given volume)
- Better music restorer
- Better video
- More overall features
- More Tweakable
- 32 BIT/ 192 KHz DAC built in
- Advanced MCACC (some say it's inferior to Audessey but I disgree and it is more tweakable post results)
- Better suited for 4 OHM speakers, the Denon may drive them but you are probably going to shorten it's life in the long run.
- Elite name for looks, but more importantly better built, better warranty than standard Pioneer receivers. Amber display with gold Pioneer badge and blue lights around the buttons. Looks amazing!
I hope this helps but like I said, either way you are getting an amazing receiver.