Copper is the better conductor of heat (so it is ideal to draw off the heat from the CPU)
where as Aluminium is a better heat dissipater (Gets rid of the heat from it's surfaces)
So a dual solution (copper base, aluminium finned)would seem to be the answer.
But thats why we have reviews, and many other factors effect cooling efficiency.
Be careful of the Volcano 7, it is a very big cooler that doesn't fit on all motherboards.
Physical size and weight tend to be a good indicator of a coolers capabilities, bigger and heavier usually winning over the more compact designs.
I must add that whatever you buy will only be part of an overall cooling solution for your system, well thought out case cooling can often have a more dramatic effect on lowering temperatures than a trick heatsink/fan combination.
After all a big heatsink and screeming Delta fan are useless if they are being supplied with a warm air supply.
Martin Just trying to help, sometimes falling short, I am only human after all.