If you're just going to do one run on a predetermined target, I don't think there is any difference. If you're trying to establish a pattern of activity in a particular timeframe when a particular body of people is in the open or something, then the surveillance or the loitering and waiting for that opening to happen, I think, is more easily handled on UAVs. It's not impossible, but they're all endurance limited and that depends on fuel and things like that. Typically manned aircraft don't have as much endurance, I think, and would need to be refuelled. They do come to a human endurance limit.
On November 27th, 2014. See this statement in context.