I just bought a Sigma 10-20 4-5.6. I bought it used but it was only a few months old. I would have been just as happy with the Tokina, and was actually looking for one; but came across the Sigma at a really good price and jumped on it.
I have not used it much yet, but can say that it feels solid, it is a little heavier then I thought it would be, the lens bag it comes with is a bit bulky and takes up too much space in my camera bag; but this lens focuses fast and is so much fun to use.
If you are buying new, give them both a try, and pick the one you like. Buy from a reputable dealer and take it back if it turns out that you don't like it. If you are buying used, just look around for a good deal, but I would go for either one.
I have not used it much yet, but can say that it feels solid, it is a little heavier then I thought it would be, the lens bag it comes with is a bit bulky and takes up too much space in my camera bag; but this lens focuses fast and is so much fun to use.
If you are buying new, give them both a try, and pick the one you like. Buy from a reputable dealer and take it back if it turns out that you don't like it. If you are buying used, just look around for a good deal, but I would go for either one.