So I am contemplating my first UWA purchase.
#1. Sigma 8-16
#2. Tamron 10-24
Sigma is wider, Tamron is cheaper and has a rebate which ends on the 31st.
I'm using a 50D and most likely won't be getting a FF until early next year. From that pov, the super wide 8mm of Sigma is very appealing and offloading it if necessary may be easier.