I found the tamron TOO sharp, sounds odd but it could have been user error as I really didn't have it long. Of course I could tweak afterwards but I prefer the Sigma 17-70, that's a cracking lens for all occasions and has been my all rounder for some time now!
D90 how many bodies to you need!!?I do keep reading good things about the Sigma 17-70mm, I just thought it was better to buy Nikon for Nikon cameras?? So I was told anyway..
Not a great fan of second hand lens'es or electricals (depending what electricals) I just think with things like a lens you run a risk when buying second hand. I found a really nice D90 in Cash Converters today and I was tempted it was only £350 but again it being second hand kind of stopped me.