Tokina AT-X 165 PRO DX AF 16-50mm f/2.8

Its almost impossible to find reviews for this lens on a Canon mount (Photozone did a Nikon-mount review.)

I was going to go for the Canon 17-55mm 2.8 (after saving my pennies) or the Tamron 17-50mm 2.8. What lead me to this lens was purely my experience with the Tokina 11-16mm 2.8 - which has just been outstanding.

This lens usually makes its way on my 7D most of the time - occassionally it'll be on my Rebel XSi.

I couldn't afford the Canon, and the Tamron's AF motor sounds like a Buzz Saw - which can be really distracting during wedding vows. The Tokina is virtually silent when compared to the Tamron, its only slightly louder than Canon's USM.

Picture quality has been stellar on my 7D, I find it sharp from corner to corner. Center sharpness at 2.8 is practically on par with the Canon and the Tamron - the edges get soft at 2.8. Stopping down resolves practially all the corner softness.

Bottom line, if the Canon is a 9.5 (on a 1-10 scale) then the Tokina would be a 9.25 - The Tokina is ever so slightly inferior in image quality - and I'm talking if you're one of those 100% crop pixel-peepers - the Tokina has MUCH better build quality - where the Canon is mostly plastic, the Tokina is mostly metal and feels a lot more substantial.

Center Sharpness at all focal lengths and Aperture settings
Best build quality in this class by far
To a layman, if you took the same picture with the Canon, they couldn't tell the difference

Edge softness at wider apertures

Canon EF-S 15-85mm
Sigma 24-70 HSM 2.8

Adorama rocks!