That is a hard question to answer definitely. The two bullets are fundamentally different. Even amongst copper solids the copper alloys used are different. Throat designs can vary a lot. My personal opinion is that our designs and the copper we use are probably better treated by slower burning powders in general because every bullet has to engage the rifling. It is at that instant where chamber pressures really elevate because there is resistance to bullet travel. Lead core bullets are "squishier" in that the lead core is much more ductile than copper so they tend to elongate while conforming to the rifling and grove diameters. Copper bullets are much less compressible so the rifling has to etch into the bullet bearing surface, and the reduced ductility of copper prevents less narrowing and elongation of the bullet as might occur with a lead core bullet. It takes more force to force a copper bullet into the rifling and so the pressure increase at that moment can be more rapid. The rapidity of that pressure rise is to a significant extent, dependent on the burn rate of the powder. A slower burn rate powder will cause that pressure spike to be "more gentle" affording the use of more powder increasing the potential of a higher bullet speed before seeing over pressure signs on the brass and primer. Another factor is the amount of energy/grain of powder that is formulated to burn at a certain rate. Double base powders have nitroglycerin which adds to the energy/grain of powder and thus achieve higher muzzle velocities for both types of bullets. Now, what do you consider "better". We can measure speed easily these days, but accuracy is just as or more important. It is entirely possible to have a lead core bullet shoot well, meaning accurately with one burn rate powder and terribly with another powder that shoots a copper bullet just as accurately. One thing is for sure, copper monolithic bullets withstand the stresses of acceleration, spin and impact much better than lead core bullets. It is possible to have very high quality lead core bullets disintegrate in flight if you push them and spin them fast enough to cause the jacket to swell and be blown away by the air rushing by the bullet. In general I would say, within a certain burn rate range appropriate for a given case, that the copper bullet would be benefited the best by the slower burning but higher energy powder. Bear in mind that this discussion is likely an oversimplification of what is happening because there are other factors such as neck design, lead angles, free bore lengths, barrel diameter tolerances, etc that we have not considered that could allow or disallow fast burning powders to work well with copper bullets.
