Depends on the setup.
With motor brakes, set the failsafe to go into neutral or it will go "crazy in reverse" like you said. If the failsafe is built into the radio, you could also set the steering failsafe so it would coast in circles until it stops (good if you happen to be going downhill
)
With mechanical brakes, I would set the failsafe to about 75% brake, so that the vehicles slows quickly (but not lock the wheels).