High rises are pretty private, imo. When I lived in one, I had no idea what was going on on my floor, never mind the rest of the building. Houses make me a little nervous, too visible, but I've done it anyway.
Hotels might be ok, but they must have CCTV security everywhere. OTOH, they want the money from the room rentals so why would they care so long as it's low key. People must use hotels for affairs all the time. I've gotten day room rates several times, out by 5:00 pm, must be a commonplace thing.
Trouble with suburban houses/townhouses is that you're kind of stuck with parking in the driveway, licence plate visible to the world. The nearest strip mall is usually too far away to park and walk to/from, and pedestrians in most suburbs would stick out more than cars anyway.
I've said it before but the fact that we even have to worry about any of this just because we want to get laid is just plain crazy. I also think it's bound to get worse as the Christian Taliban acquires more and more power. I guess all those mega-church pastors and politicians want to keep the sex services to themselves. Am I too cynical?