Depends on what sort of Landscape you take. If it is a vast panorama, then the wider primes are what you need. For landscape you will need a lot of DOF, hence you should be shooting between F5.6 and F8. In that case getting "Fast" glass is point less, unless it has exceptional sharpness in the aperture range you want.
Ultra wides have a lot of distortion, and you are better off not using them. That leaves normal wides - 20, 24 or 28mm. I prefer 28mm. The 28mm F2.8 AIS manual focus lense is one of the sharpest Nikon lenses in the 20mm-35mm range. (note that the 28mm f2.8D is a completely different glass and not all that good).
The 35mm F1.8DX is a good lens, but on a DX sensor is a "normal" and not a wide lens.
Another option used by landscape photographers is to stich the panorama using 3 to 10 shots. If the sky is not changing much and there is little wind, then that is the way to go.