Note, that the QT 7 available for Windows is still in preview mode, and there are still bugs in it (although the current preview is MUCH better than the first preview release). So, until it reaches gold status, and the adoption rate is high enough, I wouldn’t even consider H.264 for delivery to PC clients.
As far as which is better, well for 1080p and bitrates under 10mbps, I would have to say AVC is the leader. For 720p under 8mbps, Windows Media is very competitive and can actually best AVC in some cases. For 480p under 2mbps, AVC is the clear winner. And at lower resolutions, Windows Media again shines. Most of the AVC encoders I have used appear to be focusing more on HD resolutions, which may explain the better results for the most part with larger frame sizes. Windows Media 9 encoders generally try and optimize for all output sizes, which may explain why it can produce better results at the smaller sizes.