Here is the efficiency of some possible blocks or plating that can be used for heat sinks: (calculated by atomic weight / specific heat)

(Higher is better)
Aluminum: 1.114939612
Zinc: 2.568080094
Copper: 2.600081833
Silver: 4.255155819
Platinum: 7.543851508
Gold: 8.066449709
Nickel: 2.251377062
Thallium: 7.765322948

The order is in specific heat, so you can see the relation that is has. I expect that people already know which ones are heavier than others.

In conclusion this is why we see gold as the best conductor however, there are some interesting elements that are rarely ever used verses there inferior counterparts.