Actually the most effective rust remover(and I've been doing a LOT of rust removal lately) is a knotted wire wheel on an angle grinder. Wear safety glasses at a minimum, highly recommend a face shield and heavy clothing. Those wires HURT when they come off and they do come off fairly often. Hearing protection is a must if using it for more than a couple minutes.
Flap discs in a grinder work better on flat surfaces and are less painful but if there's pitting from the rust it won't get down in the pits like the wire wheel will.