Dave, I do not have the 14-24 f2.8, but I do have the 16-35 f4 VR and think it a real beauty.
A few things to consider about each lens.
The 14-24:
1) There is no doubt that the 14-24 is
the wide angle lens to have in this zoom range, or even prime range, as it is better than all/many pirmes in that range, but the 16-35 f4 VR is superb also, if used correctly.
2) The 14-24 is big and expensive and you can't use filters (easily). I use ND grads very often and consider them one of the most important filters for WA lenses.
The 16-35 f4 VR:
1) There has been talk about VR not being valuable for a WA zoom, but I can assure you it is very valuable, IMO. I took it to Europe/UK (I'm from Australia) on our recent trip there in July and found VR
invaluable for those dimly lit cathedrals and churches where f13, ISO3200 and 1/5sec were the norm. I shot f13 for DOF purposes and if I didn't have VR, I would have needed to shoot at ISO12,800 in order to get a decent shutter speed or compromised on DOF and shot at a lower aperture like f8. The other thing is that if you have the 14-24, then you need to use a higher ISO compared to the 16-35 when in low light and your shutter becomes the limiting factor. So, if you consider that you may be able to hand hold at 1/13sec for the 14-24, you may have to use 3 stops of extra ISO to get the same shutter.
2) Distortion is there but generally easily correctible in post process. I have never been in a situation where distortion could not be corrected satisfactorily.
3) Filters. The 16-35 can accept screw in filters as well as normal ND grads.
4) The 16-35 is smaller, lighter and cheaper than the 14-24, and size may be important when travelling.
Yes, the corners
can be soft if you are shooting wide open, but stopped down to f8 and by also slightly focusing toward the front of the scene rather than for pure hyper focal distance or focusing on something on the distance willy nilly, then you can counter
any corner softness.
An example of inside Gloucestershire Cathedral:
D700 + 16-35 f4 VR @ f13, 1/10sec, ISO3200.
Crop of corner showing that it is not soft: