I have the 28-75 Tamron and the 17-85 Canon. The Canon performs well on my XT and my 30D. The Tamron I have not yet tried on my 30D but is inaccurate on my XT. Having said that, the 17-35 Tamron is not good on my XT at all. On my 30D it's really quite good. It seems the XT is very finicky about which lens you use on it. When finances and the wife allow I might get a 2nd 30D.