Hi Rob
I haven’t used either, but have a look
here, the Tokina 11 to 16mm gets a great write up. Here is the verdict from
Photozone.
"Verdict:
The Tokina AF 11-16mm f/2.8 AT-X Pro DX is currently the best ultra-wide angle zoom lens for Canon EOS APS-C DSLRs. The resolution is impressively high throughout the zoom range (albeit a short one) and across the image field. Vignetting is really only a problem at 11mm @ f/2.8 but otherwise the issue is very well controlled. The level of distortions is comparatively low. Typical for most Tokina lenses it has one weakness: lateral CAs which are very high at all settings. The build quality is on a very high level and it’s a joy to handle the lens out there. All-in-all a very sound package especially when considering the quite affordable price (around 600EUR/US$).”
Cheers
Dennis