I am a Tokina fan. I started with the 10-22 EF-S and then got a Tokina 12-24 f/4. The Tokina was sharper than the Canon. Then the 11-16 f/2.8 came out that was even sharper than the 12-24. I missed the 10mm end however so I ended up getting the Sigma 8-16.
Wow, was that 8-16 a splendid ultra-wide angle lens. Close focus, very flare resistant. Unfortunately the bulbous front element made the lens a pain to deal with.
After years away from APS-C, I've returned and the first dedicated lens I've bought is the ...
Tokina 11-20 f/2.8.