If they are "ours", why do they (for a start) not display the normal regulation navigation lights and strobes, and seemingly go about their business with complete disregard for air traffic & air safety regulations? If they're supposed to be so secret, (and they must have made a pretty good job of keeping all information about them secret, despite the number of sightings), why do they fly about, in a way which suggests that they're not really too bothered who sees them? What exact;y are they doing? Testing them? testing them how? That's why they have thousands of square Miles of test ranges, well away from anyone who might see what's going on. Why don't they keep to there? Why run the risk of one coming down (perhaps in a built up area) and laying the US Air Force open to being sued for negligence, not to mention blowing all their secrets ?
Those are good points. I lived close to an Air Force base when I had my sighting, but, like you said, some sightings weren't close to military installations. It could be that they want to test their long-range and sustained flying abilities (shrug). My gut instinct says "terrestrial", but it would be cool if that wasn't true!