PrineFan,
Your best bet is to go with two fans...One in the front pulling air into the case, and another in the back exhausting air. If you're concerned about noise, buy low RPM fans (like the Panaflow's) or perhaps rheostatic switches gauged for your fans. The rheostats are nice because you can turn the fans up to full speed when you're gaming or doing other processor intensive stuff, and down (or off) when you want quiet.
If you've still decided to stick with just the one fan, I would exhaust the air. Although not as much air will move through the case, this will pull the most heat away from the processor, rather than blowing hot air into the intereior of the case.
Hope this helps!