In general, it is a good idea to buy something that has the features you need, and then look no further up the receiver line. If you need more power, you should be looking at a receiver with preamp outputs and a separate ąmplifier or more than one ąmplifier.
Yamaha is a good brand, so I don't think you will go wrong in choosing it. Pioneer is also good, so I doubt you are going to be dissatisfied either way. I do recommend buying from an authorized dealer, so that you get the manufacturer's warranty.