What is the best focal length of wide-angle photography in desert?

In a place like desert, telephoto is more useful than wide angle. Since you have 20f 1.8, take this one. You don't need to exchange it for a wider one. After all, the wider the angle of view, the less useful it is. As for the aperture, landscape photos are usually taken with a small aperture. The aperture of F 1.8 is very large, even if it is dark, it should be enough to shoot something. If it is not enough, there will be a shelf. And even if the aperture is bigger, it will reach F 1.4, which is not much bigger.