I'd also vote for resin. Lighter is better, and less risk of tipping or fumbling it.
That said, I'd also vote for a long and deep connection point that's got enough room to put at least a pair of some heavy duty rare earth magnets in each side, so that they can be removed for storage and transport. Something at least an inch long and half inch wide and deep, with enough material to mount some 1/4 inch or even 3/8th inch wide and 1/8th inch deep magnets. That's enough sticking power to handle anything up to a half pound or so of material, especially with a deep socket to prevent twisting.