I have had the 3312 for a couple of weeks, replacing a 4 year old Pioneer. I personally have not looked back, and am very pleased with the performance.
I think between the receivers you have mentioned the 3312 offers the most in terms of overall value and performance. The 3312 is 125 watts per channel, on all channels. The Marantz and Pioneer are 110 watts per channel.
I personally found the sound quality on the 3312 superior to my Pioneer. I also think Audyssey is a better calibration tool than MCaCC on Pioneer. I would think sound quality on Marantz would be on par with Denon, since they are owned by the same company and share many traits on the various models. In terms of features, the Denon can't be beat.
The Denon and Marantz are both 7.2, the Pioneer is 7.1.
I think the new GUI on the Denon is far superior than what my old Pioneer had, I can't speak for any new Pioneer GUI.
Obviously I made my choice,if I were picking between the units you mentioned I would still chose the Denon 3312.
Since I can't speak about price in this forum, lets just say the 3312 can be had for a very appealing price.