17-40L if your budget is under 600$. @ F/8 it's just fine.from what I have seen zeiss is top for me, but pricey, right now I'm leaning towards 16-35 f/4, 17-40 is not really interesting for me since it's old lens and new 16-35 is much better and not so much more expensive...
16-35 F/4L is the best option at the moment. Sharp, IS, and relatively inexpensive. The zeiss 15mm would be negligible in IQ, perhaps better micro-contrast but really pricey.
TS 17mm if your really into landscapes and got the budget for it.
buuut back in my mind there is still possibility of new UWA presented in photokina
Depends on how much you rush for it. If (and that's a big IF) such lens is announced at Photokina, it will take weeks, perhaps months to get it on the shelves. If you do not have the need for f/2.8, I'd go for the 16-35/4L IS if I were you. It complies with the requirement list you originally posted quite nicely IMHO.
I'm fully aware of that it won't be available immediately...