I own a Tokina 17mm and love it to bits! (Had the FD version as well.)
For me it allows for a nice architectural image without needing to tilt the camera up to include the top of the image. I can crop afterwards to remove the extraneous part of the image.

It is wonderful for landscape work that is sharp front to back. By far, this is my favorite extra-wide, wide angle lens.

- Nanette