While I do not yet have a large, calibrated monitor for viewing and evaluating, I am happy thus far with images I have shot with Nikon-fit Tokina 17mm 3.5 lenses. (One AF and one MF, now discontinued.) The current Tokina ultra-wide zooms have been well-reviewed at several sites. I elected to purchase the Canon 10-22mm EF-S, for my Canon DSLRs, but seriously considered the Tokina 11-16mm, and as I enjoy this type of lens so much, may well try the Tokina eventually.
While it is not ultra-wide, our Tokina 100mm 2.8 macro lens is very sharp and clear, with less apparent distortion than my Canon 100mm 2.8L Macro! The out-of-focus areas are beautifully rendered. Tokina does make some really good lenses; one must, of course, look for reviews to see which are the good ones.
Canon 5Ds R/7D2/7D/5D/40D/1D2N; Nikon F6/D3s/D700/FM3A/Coolpix A. Lens selection undergoing changes; some favorites: Zeiss 2/135 APO Sonnar, Canon 100mm f/2.8L Macro IS and 135L, Nikkor 14-24/2.8G and 200/2 VR.