Best 383 valve cover gaskets to stop all the leaking

How about a little more info? Iron heads with a questionable gasket surface? Aluminum heads, with a nice machined surface?
What covers? Cast? Fabricated ?old steel stockers? Steel repops? Chrome? Paper thin stamped aluminum moroso's?
Have you checked if the covers are flat? Are the bolt holes out of shape from over-tightening? Are the valve cover rails of the heads level, checked with a straightedge?
More info=more help.