I have grown to like ultrawide lenses (both rectilinear and fisheye). The first UWA lens I had was the Sigma 10-20 f/4-5.6 which I liked for its extreme wide angle (as in the shot above) and its sharpness, but it was just a little slow. At that time I was using the Fuji S5 which doesn't have a great high ISO capability, often resulting in blurred shots of people. That's why I traded up to the Tokina 11-16 f/2.8.
I've had the Tokina 11-16 for a while now and am happy with it. It's very sharp and the fast 2.8 aperture is handy for low light. As a bonus, it can be used on a full frame camera (at 15mm or 16mm, as in the shot below on a Nikon D3) although the edges are very soft. The only minor complaint I have is that it has a lot of chromatic aberration (which can be corrected in LR).
Meanwhile, I've wanted to have a lens that is a little more versatile. The Tokina 11-16 is great as an ultrawide, but for general purpose shooting, the 24mm equivalent at the long end is often a little too wide for me. I thought about trying the Sigma 10-20 3.5, which I've heard good things about (according to DXO it is as sharp as the Tokina). The 30mm equivalent seemed like it would be useful for me. When I had the Nikon 28 1.8G, I enjoyed shooting with it, and I like shooting with the sigma 35 1.4 on full frame.
I just received it yesterday and it brought back pleasant memories of the Sigma 10-20 f/4-5.6. I hope to do some testing with it soon and will post comparisons, especially as to whether the extra length is useful.