I use the bumper cam if I'm serious. If I'm just taking one of my over-performing cars to the Capri Rally for quick cash, I'll play around with the other views.
I find the upside to 3rd party cam is I get to see more of the territory, the downside is it makes me feel too removed from what's going on (I don't drive my real car from a spot 15 feet over and behind it, so it's kind of weird to drive these "cars" that way)
The roof cam is a good compromise, but I've come to rely on the rear view mirror that's only in the bumper cam.
