i use silicone/plastic spoons designed for this job (or for eating icecream
). either way works, it is all a matter of how comfortable and experienced you are with each method.
I dislike "blob and press" because you can never be sure which direction it will go, and you can't be sure the cavities of the heatpipes will be filled.
"Spread up, spread down and sandwich it" is what i use, though it might trap pockets of air.