Well it's always a good idea to have an even setup.
So get a nice heat sink, but also have a nice fan to go along with it.
If I had to go "high end" for one and "low end" for the other, I would spend the money on a heat sink.
Heatsinks are better for cooling but that doesn't mean that a nice fan would be to much either I mean I would probably put it a good HS and a good fan.
The fan cools the heatsink, by the way, not the processor. It is the heatsink that absorbs the heat generated by the processor. The fan just moves it away.