I found two allen keys are the best and cause the least damage. The closer the exact size the better, too small and they will tilt causing damage same as pliers due to the angle. Of course, if someone has tightened them up then good luck not damaging them.
This one, Shimano TL-FC20 one end for the dust caps the other is for the slotted side of chainring bolts. Not expensive and gets a surprising amount of use, if you come against a stuck chainring bolt it does the job every time.