I own both a Nad and a Yamaha. I like the sound of the Nad more. The Yamaha is currently in the repair shop, but this may just be an isolated incidence. The Nad will have a warmer soundstage and the Yamaha will probably have more features. Both are nice.
It depends on usage. If the system priority is HT performance, the Yamaha has a much more extensive feature set and it does do a decent job with music. OTOH, if music is the priority, IMO the NAD would be the choice. I think the NAD is much more musical than the Yamaha and has better amps.
FTR, I have never listened to these receivers in the same system and as always, YMMV.
Being an owner of both lines (former Yamaha RX-V995 and currently NADT163) I'd say get a chance to listen to both units, especially if you can borrow the Yamaha and NAD receivers. The NAD is wonderful with music. But it also does an excellent job with movie audio. Listen to both if you can and then decide.
I have a Nad T762 and I'm totally pleased with it both for music and movies. I wanted to warm up the sound a bit since my speakers tend to be on the bright side.