I've been a Pioneer user for the past 8 years, I just switched to Yamaha about 2 weeks ago. My reason for switching was due to issues I've had with my pioneer AVRs, Yamaha's have a reputation for being one of the most reliable AVRs.
Like all things in life, there are advantages and disadvantages.
Things I like about Yamaha:
-Better OSD layout
-Easier to navigate the menus and find what you need
-YPAO EQ is much better if you do your own tuning with REW etc(you can vary the Q and frequency of the filters).
Things I like about Pioneer
- Better remote(programmable, backlight)
- MCACC lets you have 6 different EQ profiles that can be switched on the fly and customized.
- MCACC seems to do more steps than YPAO but i can't be sure
It comes down to features, layout etc. Both companies know what they are doing and will deliver good sound.
Main System: SVS Ultra Towers - 15" custom ported subwoofer - SVS PB-1000 - Yamaha RX-A740 Aventage. 125dB @30hz, 16hz @ -3dB
Computer System: Carnagie Acoustics CSB-1 - 12' Onkyo sealed subwoofer - Pioneer VSX-92 THX
Other speakers owned or auditioned: Aperion T6 - Ascend CBM-170 - Energy RC-10 - Wharfdale 10.1 - Arx A1b