I have found I prefer photographing alone, most of the time. I feel I make my best pictures when I am in my own psychological space, and that is something hard to achieve with other people around. Sometimes being out with other photographers give me a little performance anxiety . . . they know what was there, and they are going to see the result, and I just can't take that kind of pressure . . . jk. Most of the time when I am out with other photographers, I want to just shoot the bull and not really do any work.
But, in general, I would prefer to be on a road trip with someone who is a photographer than who is not. With photographers, there is a common understanding of what it is that makes us set up the camera, no matter how ridiculous.
Lately I've been combining trips visiting my parents with photographing. They are always very understanding while I take forever, moving two inches in one direction or another, or waiting for the wind to stop blowing, or my wanting to get out and look every five minutes. They read, pick up cans and bottles, collect rocks, make me sandwiches . . .
Girlfriends are another issue though. I will never go out with a camera and girlfriend . . . made that mistake too many times.