Either is probably okay. But they do have different other inputs, and so it will also depend on what else you have and want to hook up. For example, the Yamaha has two component video inputs, and the Pioneer only has one. That will matter if you have two things that you want to hook up that way, but otherwise it is irrelevant. The Yamaha also has more other analog inputs, which may or may not matter depending on what you want to hook up to it. So you need to tell us what things you want to hook up to it, and the types of connections that are possible with them, in order to give anything like definitive advice.
Here are a couple of articles about them:
2013 Pioneer VSX-xx23 Series A/V Receivers Preview | Audioholics
Yamaha RX-V473 and RX-V573 A/V Receivers | Sound & Vision
Normally, I personally would probably go with a Yamaha, because they tend to be very reliable. However, I often forget about Pioneer, which is worth considering at your price point. I would want to read up on the video processor in the Pioneer before I rejected it, as it might be the better choice at your price point. But if you don't have any analog video that you will hook up, that might not be terribly import for you either.
