I was hoping to avoid the weight and size of a WA zoom but I am starting to reconsider my choices. The 12-24 f/4 appears to be a good alternative and it actually bridges a gap in focal lengths for my existing set of lenses.
I had tried the Sigma 15-30 DG EX but I was very disappointed with the soft images and flare. This was my only non Nikon lens .
I prefer to keep all my equipment Nikon and will purchase the 12-24 f/4 as soon as I can find a good deal.