The autopilot comes out on top here because it doesn’t have an instinctive aggressive response. If the aircraft is in trim then in a severe turbulence encounter doing pretty much nothing is IMHO absolutely the safest thing to do if the autopilot disconnects. Interestingly Airbus recommend manual thrust (ie set it and don’t touch it...) in situations where big speed changes cause the auto thrust to hunt for the target speed. Speedbrake can control speed approaching MmO.