rc-monster heatsink

[BrianG]

I would say the RCM heatsink since it has more mass and fin area from what I can tell. You could always run both and see which one provides cooler temps. To get maximum benefit, it helps to put a little thermal compound between the heatsink and motor. Just a little though since it will spread out, you don't want too much or it'll squish out and make a mess.