If your 17-35mm f/2.8 is still giving you results you like, most replies say not to switch based on MTF charts alone. Charts and reviews aren’t a good reason to replace a lens unless you have a specific problem to solve.

Main tradeoff: moving to the 16-35mm f/4 VR gives you VR and a slightly wider 16mm end, but you lose a full stop of maximum aperture. That extra stop from f/2.8 can matter a lot, especially for low light or any situation where subject movement is involved. VR helps with camera shake, but it does not replace the benefit of a faster aperture.

So the practical question is how you shoot: if you value the brighter f/2.8 aperture, the 17-35mm remains a strong choice. If you specifically want VR and a bit more width, the 16-35mm may make sense.

Several answers lean toward keeping the 17-35mm unless you’re actually unhappy with its sharpness or have already exhausted technique improvements. If budget and needs justify a bigger change and you want an even wider option, the 14-24mm is the aspirational alternative mentioned most favorably.