Of those two I would get the Denon and that's saying something since I am a fan of Yamahas! I would go for an Onkyo TX-NR818 over either of those boxes tho. Better room correction and much more grunt. The current Onkyos seem to not have as many probs as previous generations so I wouldn't let reliability be a deciding factor if it was me (not guaranteeing any particular option won't break tho). Even better would be the TX-NR1010 which some guys on the official owners thread have found for less than your budget cap. It weighs more than twice as much as the RX-A830.
Just my 2c