Hi skelter! Nice question at just the right time. I did a big super-wide-angle zoom shoot-out this summer here
. Not all details have been filled in, but you can get the gist of the results already and have a look at the respective test-shots I made.
The Tokina 10-17 is not
in that comparison as it is a fisheye-zoom
giving all curved lines. You can see professional reviews of that lens here
If you already have a 18-XXmm zoom, I understand that you want the widest. Same situation with me. And as you can see from my signature (btw. please add one in your profile for you with your gear too) I opted for the Sigma 10-20mm for straight reproduction
and the 10.5mm fisheye for the widest possible fov.
As you probably know curves from fisheyes can be straightened with postprocessing tools but the results are unsharp at the borders and corners. See some examples from my fisheye originals
defished in CaptureNX here
Addendum: The fov on the Tokina 10-17 is "180 degrees (diagonal) at 10mm to 100 degrees at 17mm", the fov of the Nikon 10.5mm is 180° diagonal and the fov of the Sigma 10-20mm is 102° - 64° diagonally.
Hope that helps!
Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews
, My Pictures
, My Photography Blog