Red ones for sure. They are for CPU. What's your plan for fastening it ?
The riser (left object in the picture) will sit on the mosfets with some adhesive thermal tape in between. The heatisnks will be fixed to the riser with 3 screws and some themal paste between. I'll bend some hard wire, it will go between 2 fins of the bigger heatsink, curl around the cpu mounting bracket screws and fixed with nuts (left nut on the picture and the one below it)