A situation we all hope to never have: engine quits at a low distance AGL.

What bank angle will produce the least altitude loss for a 180 degree turn?
Is this common for all aircraft?

Readings have shown the elevator/wing to be more efficient at turning the aircraft
than the rudder alone.

It would seem better not to try to hold altitude on the turn, but one still must avoid stalling
the wing. Airspeed is also a factor in gliding efficiency.

What is the best way to turn 180 degrees with least loss of altitude?

Some good references provided. Curious about rudder technique in a steeper bank. At 45 degrees, rudder is pitching nose down some, but should be there to "follow" the wing around the turn (lowest drag). Some elevator, some rudder to swing the tail through the yaw plane, giving up some altitude, so as not to load the wing as much (like an emergency descent)?