Question : Problem: Should a cpu fan pull air from the cpu or push the air down onto it, to cool it.

Should a cpu fan pull air from the cpu or push the air down onto it, to cool it.

Answer : Problem: Should a cpu fan pull air from the cpu or push the air down onto it, to cool it.

Depends on the design of the heatsink! I guess that for a very general idea, blowing air onto the heatsink may be more efficient, as the airflow is a bit more "intense" and it *may* be better from a dust-accumulation point of view, but there are a lot of factors involved here.
/RID