Don't rule out the Promaster 19-35mm. I had it and the Tamron side by side and the only difference was the grip patterns and logo printing. Everything else was identical. The Promaster cost slightly less and came with a 6 year warrenty (Tamron is 5 years). I bought the Promaster and it has performed very well.
tuanokc is right though, if you want the best, you can't beat the Nikon 19-35mm.