I'm using marantz and very happy with it. amp section is quite good. the dsps are very good, Dolby PLII gives a pleasant effect, IMHO.
I have heard Onkyo and Denon during demos. Denon is more suited for movies, in my opinion. Onkyo, I think their higher end models are good; not very impressed with their low to mid range models.
in short, my vote would be marantz for music and denon for movies, out of the given choices. but leaving the options, I highly recommend you to go with AVRs that can decode Dolby TrueHD and DTS HD master audio, to be a bit future proof.
good luck.