Onkyo has very low multichannel power (~5x35W) so if that's a concern I would definitely get the Marantz. Actually the only reason to go for Onkyo would be the Nettune LAN feature.
It really depends on the usage of the receiver, music is hands down the Marantz, and Ht would be the Onkyo. Although the Marantz will do very well both areas, so if your in the middle(50%music/50% HT) go for the Marantz.
Speakers also come into play here, post back with some more info and we can give a better response!
thanks to everybody, G.DawG; here is my system, Marantz DV6400 DVD Player Wharfedale Valdus 400 Front Valdus 200 Surround Valdus Centre Speakers, Diamond Cubic 10" Sub. if you give me info ,I ll be happy. Thank you very much...