There's quite a bit of math to be done when you need to calculate a size for your heatsink.
As there are many options to choose from if you don't know the size yet, is it just better to pick the largest one? (assuming you have unlimited space for it); Example
The other option would be to use a smaller one but with a fan for forced airflow like this one.
So is it more efficient if I put a small heatsink with a fan or just use a large but not 100x bigger heatsink?