In reply to davidbeynon:
I got the Nikon 16-35 F4. I did a LOT of research, tried all those mentioned (except the 10-20sh options) and eventually decided on said 16mm zoom. Admittedly, it does have some distortion but it's incredibly clear. Distortion is easily fixed w/digital and to be fair it's a usual attribute of a WA zoom. Some plastic components are a put-off and it's corpulent but it's by far my fav. lens I've ever owned. See what Ken Rockwell has to say these days, I'm out of touch with him but he does thoroughly test lenses.
If you really want the ability to use on a FX, I strongly recommend the 16-35mm. If you can reside at the DX sensor (I couldn't), then consider the Nikon 10-22 (or 20?) as this is a really REALLY good lens and will offer the same field of view at the 16-35 on a FX.
Obviously, the 14-24 is the gold standard, second only to the 14mm prime (it has less distortion at the corners on FX). But in reality, you'd struggle notice any difference. The 20mm AF-D is also a good option, but not wide enough for me.