I've had both. Used to own the 50D and bought the 10-22 for it. No complaints. It was a good lens
Now I have the 7D and bought the 8-16. I'm a wide-angle lover, so the extra width grabbed me. I tested it out in the camera shop taking pictures outside along with a 12-24 for my 5DII. The 8-16 was a better sample, so I bought it.
I would say it is every bit as good as my 10-22 and it is slightly better than my 17-40 on the 5DII
No CA to speak of, flare minimal if at all. You may want to check out my posting to DPReview a while back:
http://forums.dpreview.com/forums/read.asp?forum=1029&message=36559792