The Onkyo has it's advantages and the Sony has it's advantages. The Onkyo going to deliver more real power than the Sony, but chances are the Sony will have enough power to satisfy your needs. The GUI on the Sony is a bit more graphical than the Onkyo. The Onkyo seems to favor a very basic monochromish GUI while the Sony is more intuitive. The Audessey 2EQ on the Onkyo should be substantially better than what the Sony model offers, although I honestly don't know much about Sony's auto calibration as it isn't talked about in audio circles that much.
The Onkyo also has an advantage in connectivity (more inputs than the Sony, especially for HDMI). Another plus is the 2nd Zone capability that the Sony does not have. Sony's version of Zone 2 is their S-Air components, but you are limited to using only S-Air components to get second zone sound in other rooms, meaning you are stuck with tiny little plastic speakers.
It seems you have a trend of buying Sony, so getting the Sony won't be a bad choice for you. However, Sony has a bad rap for home audio products. They do offer cheap yet halfway decent speakers, but they aren't doing anything innovative or providing a good mass production speaker system that people actively look for. Sony still makes speakers for one reason, people buy them based on the name. If they where any more expensive than they are they'd certainly not sell. They tried that once with the ED line at Circuit City (a good speaker line actually) but the stigma of poor quality speakers kept them from selling, and it also kept people that where looking for the typical cost effective Sony speakers from buying too. The models from the ED line where very competitive with the crop of speakers at the time and offered a lot for their money too, but people just didn't accept them.
Sony receivers are hit and miss, however I've noticed one constant trend with Sony's receivers. They don't have a lot of headroom. Nearly every review that has measured wattage output of one of these Sony receivers shows a serious lack of output compared to other receivers in the same price range. Onkyo has been consistantly setting the bar for high output in all price ranges. You may not need the extra power, but the Onkyo will have it. This could be especially useful if you decide to change speakers at some point as well.
