A really good price on last year's model. These are really good receivers.

It all depends on what type of sound one's ears are used to. I was exposed to Denon amplifiers when I was growing up and I kind of like them. Denon amps sound aggressive and accurate with good speakers. I guess they have a wide dynamic headroom. Yamaha amps are the opposite of Denon amps but I have never had an Onkyo and wonder how they might sound.

grew up with kenwood receivers, the inventors of home theater 1981
I miss their home products which are not made any more, still own the VR 2090 and VR 2080 awesome receivers, first to hit the market with DTS sound in the late 1990's.
Onkyo seems to be one of the leaders these days in home theater receivers, but never owned one yet.
Still own the KENWOODS for almost 13 years (killer sound)

I'd go with a Denon any day.. not just ANY Denon but with a few select models like the 38xx series for example.
Denons which have a much larger fanbase and as #2 said, they have a larger dynamic spectrum than similarly priced Onkyo cousins.