I had a Tokina 17mm (FD) that was an absolute joy to use. When I switched to the EOS system, I grabbed the EF version, which IMHO, is not as good. I offloaded it when I purchased a 17mm TSE, but always wanted a 17mm Tamron.
I found myself missing the smaller lightweight version (the TSE is far too bulky to carry around when shooting landscapes and late last year, I landed my "dream" non-OEM ultra-wide, the Tamron 17mm SP. This is the early version (1979 build), with in-built filters, no plastic covering on the f-stops and the rubber grip matches the early 28mm I also own.
This 17mm is outstanding and I highly recommend it to anyone who is after a cheaper alternative to OEM wides. When first released, it was more expensive than the Tokina and Vivitar, and after using both the Tokina and Tamron, I can definitely see why. The specs for this amazing lens are here:
Tamron 17mm SP Adaptall Lens
I've been a fan of the Tamron Adaptall lens system since I purchased their outstanding 180mm f2.5 Anniversary Edition lens, when it was first released in 1988. The hardest part of leaving the FD world for EOS, was offloading my Tamrons: 300mm f2.8, 90mm f2.5, 180mm f2.5 and the 28mm f2.5. In fact, I missed them so much, I ended up buying a 28mm only a few years after selling mine.
I now run both with original OEM Tamron EF mounts - they actually cost me more than the lenses they're mounted on . . .