My stopping is usually for a few hours sleep, restocking of food and whatever, and moving on, so the Walmart option or rest stop works well for me. I never pay for a campground for a rest stop, there's no need to with a self contained unit. Had I wanted to pay for overnight accommodations, I would stay in a hotel room. If at a Walmart or other similar stop, I usually buy what I have to first, then rest, so if I have to leave on short notice for any reason, I just go. I figure that security is bound to be less harsh on paying customers. I do pick areas with video security coverage. Not too many problems in areas where what is done is recorded. I don't avoid a Walmart in favor of a remote peaceful pull-off. I think there's more of a chance for problems in remote areas where what happens is unseen. If I'm asked to move on, I do so. No big deal. I never get the lawn chairs out and set the awning like some folks I've seen.
I like the rest stops down on Rt 95 in the Carolinas where there are darkened areas of the parking lots for sleepers, although I always question safety in darker areas. The rest stops are well traveled, so the chances of something happening and being unseen is remote. One of the states (I think Virginia) closed their rest stops (maybe for financial reasons?) which I feel creates a hazard by not allowing people a place to stop and rest. Fatigued drivers are dangerous to everyone.
It is a shame when one can't rest in a rest stop.