I would go with the 4311. While both are 9 Channel AVR's and both offer Audyssey MultEQ XT32/SubEQ HT, there are some differences. The Onkyo offers THX Post Processing as it is Ultra2 Plus Certified. In addition, it does offer outstanding Video Processing with the tandem of HQV Vida and Marvell Qdeo. However, it does run a decent amount hotter than the Denon does. Especially if the AVR is going to be placed in an area without excellent ventilation, the heat can be an issue.
The Denon supports up to an 11.2 Speaker Array whereas the Onkyo can only do 9.2. Granted, I find it hard enough to setup a 5.2 HT with proper placement, but some have the space to support it. In addition, not only does the Denon run cooler it also offers a Preamp Only mode where the Amplifier Stage is taken offline when using Outboard Amplification. Reliability has been quite good with the Denon and future resale value will most definitely be on the Denon's side.
Both are excellent AVR's, but I do think the Denon is a safer bet. While I personally use an Onkyo TX-NR3008 strictly as a Preamp and could not be happier, some have not been as lucky as me in terms of reliability.