Comparing the ultra-wide crop-sensor camera lenses is an extremely difficult task, so I’ll put the summary first: they all deliver excellent image quality and you can’t go wrong with any of them. To my ‘just taking pictures’ assessment, they are all excellent. There are some differences though, so I’ll try to point those out so you have a better chance at choosing the one that’s best for you.

• The Sigma 8-16mm f/4.5-5.6 is the widest (and remember, 8mm is 20% wider than 10mm, so it’s a very real difference). Not quite as sharp in the corners as the others, and lower maximum aperture, but it’s really pretty good, especially considering it’s the widest of the wide.

• The Sigma 10-20mm f/3.5 has a bit more distortion than the others but delivers very nice images. It has a great build quality, and does pretty much everything well.

• The Tokina 11-16mm f/2.8 gives you the widest aperture if you’ll be working in low light (with ultra wides, depth of field is rarely an important point), but it’s a bit soft at f/2.8, so the aperture advantage isn’t huge (I usually shoot it at f/3.5 if I can to get it sharper). It has very little vignetting and distortion, probably the least of the group. Unfortunately, it does show quite a bit of chromatic aberration at times. Overall it may be the best image quality of the group.

But like I said above: they’re all excellent. We hardly ever get anything but happy comments about any of them.
May, 2013