Both are great sounding receivers and very comparable. The Marantz uses Audyssey room correction while the Yamaha uses its proprietary YPAO. The Marantz has Airplay built in which if for streaming audio wirelessly to your receiver from itunes. The Yamaha can also stream wirelessly from your Ipod/Iphone but not as effectively in my opinion as Airplay. Features to features is a wash between these two choices.
Now, you may need to consider which speakers you have and their sound characteristics. Because some receivers are brighter while others are more neutral. So this will effect how your speakers interact with the new receiver. The amp section on the Marantz may be a bit more robust than the Yamaha as well. So depending on the sensitivity of your speakers, this may make your system sound louder.
Lots to consider. If it were up to me with these two choices, I'd order/but from a place that doesn't have restocking fees and buy them both. Return the one you like less.