There was a thread about this recently:
http://www.iceinspace.com.au/forum/s...d.php?t=128380
I considered the QSI 683 and the QHY9 before I bought my SBIG STT-8300M. From my research I had considered the QSI and the SBIG of equal quality and capability and ultimately I went with the SBIG because I thought the whole package, with self guiding filter wheel and adaptive optics, was a bit better.
A less important factor, though still relevant, was that the SBIG came with CCDSoft and as I was happy with all my other software (for mount control etc) I didn't want to spend another ~$500 on Maxim or TSX, or whatever, just for image capture.
There's also the Atik 383 which I haven't used, though I was really impressed with the quality of my Atik 314L+, and I really liked the included Atik Artemis capture software.