I own the 16-35, 24-70, 50 f/1.4 and 70-200.
The 24-70 is my most frequently used lens. Quality is very good at all focal lengths. It's an all purpose lens - good for landscape and portraits although I prefer the 70-200 for portraits. I do find I need the widest end a lot, so either the 14-24 and 16-35 are necessary counterparts for landscape work.
I chose the 16-35 over the 14-24 for two reasons. A lot of my landscape work involves water and using the Singh Ray Vari-N-Duo to slow exposures. The 16-35 has filter threads and the 14-24 does not. There are workarounds - but none as simple as the 16-35. I rarely need to shoot it wide open so the lack of f/2.8 is a non-issue.
The VR aspect of the 16-35 has been important for me. I have used it in some interiors where tripods were not permitted. I bought it specifically for use on the water where tripods did not provide stability due to the movement of a canoe or ship.
I've tried to substitute the 16-35mm and 50mm for a 16-35 and 24-70 on a couple of occasions - in the Okefenokee and in Venice. In both cases I came away a bit frustrated and wished I had the 24-70. It is possible to use the 50mm to fill the gap, but whether it works really depends on your style.
If money is an issue, one under appreciated lens is the Sigma 15-30. It's a relatively recent design for film and FX cameras. Like the 14-24, it does not have front filter threads, but it is pretty economical for thewidest end if you choose a Nikon 24-70.