I've been using the Tokina 12-24 F4 on my Nikon D7100 for a few months now. It has quickly become a staple of my photography kit because of the quality results it can produce.
I had some time this weekend to put together some thoughts if you're considering a new wide angle for your bag.
Solid build quality with weather sealing on par with Nikkor lenses
Greater focus range vs. the Tokina 11-16 F2.8
Focus is incredibly fast
Incredibly sharp throughout the zoom range, even at F4
Autofocus performs very poorly in Live View on my Nikon D7100
DX lense only, will not work on Fx cameras
As you can see from the gallery of street photos, the Tokina performs incredibly well during both the day and night when shooting in urban settings.