Not having a whole lot of experience with Yamaha receiver (besides shopping/auditioning them) I won't make any comments there. However, I will say that Sony's ES line is waaaaay above their standard line and more directly compares to Yamaha.

If you have the chance, find a local store that has both and audition them. For a more accurate comparison, make sure both do NOT have soundfield settings enabled, other sound enhancers, bass/treble set to norm etc. You can always listen to the frills, but you can't judge the quality of the sound with one amp juiced up with all sorts of internal processing and the other on direct stereo bypass.