Silver for everything, it's the best electrical and thermal conductor (metalic) and the oxide is even better as a conductor.
Silly question? If cost were no object and you had your pick of all the metals out there?
What metal heatsinks the best? I'm curious.
I don't know if a copper-aluminum junction has necessarily higher thermal resistance than an aluminum-aluminum junction (certainly, an all aluminum light that was milled from one piece of aluminum with no "gap" would have lower thermal resistance), but even if it does, another issue that should be considered is heat capacity:An Al heatsink would be good with an Al light where there is good thermal contact between the heatsink and body of flashlight. A nice copper heatsink meeting the aluminum body of a flashlight might tend to cause the heat to load up in the heatsink due to the lower thermal conductivity of the al body. Am I correct here, mostly?. I guess that might depend on the grade of aluminum, some al grades conducting heat better than others.
Bill
Obviously not a metal, but Diamond is meant to be pretty good.