Before I bought my 24-105, I also considered 28-135 which has the first generation IS (they say it only offers 2 stops of image stabilisation). Both 17-85 and 24-105 have 2nd generation IS (3 stops).
I used to own the Sigma 18-200 (non OS) and it almost always gave me yellowish picture colour (sent back to Mr. Jessop). I guess the new version has the same optics, just with added OS
I also owned 17-85 which was not sharp on the wide end, and it also sucked dust like a Dyson... mR eBay sold it for me!
I also read that the 28-135 never rivals the IQ of 24-105 and it also sucked dust like Mr Hoover!
My suggestion is get the 24-105 and be happy!
40D, 400D, 24-105L, EF 50 1.4, 580EX MKII, EF 100 f/2.8 Macroe, EF 85 1.8 (on order)