As someone that had a rack on the back of their car, I could secure it, but I don't like the marks it left on my last car.
As I get my focus, I think I am going to go for the trailer hitch and rear bike rack - less aero drag when you're not carrying something (as the bike carrier isn't installed, but the bars and rails up top are always installed), and you have the option to add a small trailer for a kayak, canoe, or platform for a cooler.
But I am open to hearing that on top is better for some reason.