Depends, I guess. I tend to lean a bit towards humans, since most of the famous landscapes coming to mind now do have some people in them.

Most landscapes are trying to focus on nature and its beauty or danger or some other trait. Depending on the subject matter, adding people might convey this feeling better. You can paint a stormy, icy sea to show nature's fierce side, and that could be made even more potent if you throw in a broken ship and some drowning guys. You can paint a peaceful pastoral landscape, and if you add some little relaxing people under a tree, it might be easier for the viewer to sense the "message" of the painting.

I guess people in a landscape are there to add a human perspective, to help viewers get a stronger feeling and ability to relate to the work.

No people. Although the people could bring more perspective to the dimensions of the elements, at the same time it could reduce the impact of the first impression because human presence makes it definitely real.