Which head/combustion chamber is better for performance? Speed master aluminum LA or aftermarket magnum iron head?

For all out, one of the newer aluminum castings. The best between the OEM castings? Shaft mounted rockers or stud mounted. Shaft is more stable. Closed or open chambers? Pretty sure there are available pistons that can help the open chamber. In the end, I wouldn’t sink a dime into a cast iron head if I wasn’t required to.