Bumper cam all the time.
* It's the same perspective as cockpit view, but with better visibility
* It's the only view with a properly sized rear view mirror (essential for close racing)
* It's the only view with analog gauges which are essential for precision shifting
* If you drive in real life, you never stare at the hood of the car, you are always looking down track...so hood/roof cam isn't necessary.
* It only takes a few laps to learn the width of your car and how to place it properly on the apexes.