I was looking into what heatsink I should use for a portable Wii I'm working on, and I found that there was a few different types of materials that are used for them. So, what material dissipates heat better?
Copper conducts heat through itself better than aluminium, but aluminium fins shed heat just as efficiently as copper fins. A functional minimum cooling setup for a 4 layer Wii will average in the mid 40s (celsius) whether the sink is copper or aluminium, so it doesn't really matter what material the heatsink is made from. Most people use anodised aluminium heatsinks, and then stick them to a 2mm thick copper plate with thermal paste if more surface area is needed. The copper plate will spread the heat across itself for the aluminium heatsinks to pull up and out. It's just as effective as a full copper setup, and much cheaper.
4 layer Wiis run very cool compared to modern systems, so the minimum cooling for them is very forgiving. The G-Boy uses a 30x30x10mm blower fan with a single 25x25x10mm aluminium heatsink on a 2mm thick copper plate, and you'd still be hard pressed to get it to overheat under normal use. The Ashida takes it a step further by using only aluminium heatsinks, but using 2 large ones with an axial fan to achieve total overkill.
Heatsink physics are complicated. But in it's simplest terms... more conductivity, more surface area, and more airflow all play a role. The more of each, the more effective your cooling will be.
For the Wii, you are looking at under 10 watts, so there's not a lot of heat to dissipate. Copper is very heavy, and the results are diminishing. Aluminum should be more than sufficient, as long as you have effective contact to transfer to the heatsink, a decent amount of surface area, and some airflow across the fins.