Hi. Do they both have everything that you want? For example, do they both have all the connectivity that you want? Consider that the Pioneer only has a subwoofer pre-amp output, while the Yamaha has 7.2 pre-outs. The Yamaha also has more HDMI inputs/outputs.
My personal opinion - I'm a Pioneer fan, but I'd go for the Yamaha between those two...especially if you're paying full retail for the Pioneer, which you would be if it's $550.
EDIT - You can get that Pioneer for less than $550, at least in the U.S. As one example, Amazon has it for $497.