Had roof mounted Thule Proride's on the old car, but went with a towbar mounted rack on the new car. Towbar is detachable and the Thule rack locks down with just a lever – takes just a couple of minutes to put both on, or take off. Roof mounted was a faff to take on and off and the temptation was to just leave it on all the time, which shouts that there's a bike stored at the house to any passing crims, as well as affecting fuel consumption.
Towbar mounted feels safer and sturdier too. Tilts for easy access to the boot. Much prefer it. I just hope nobody runs into the back of me.