System Pressure?

I just picked up an 84cfm case fan for my computer. It's got way more kick than any of my other fans. So I was wondering, should it be in the back pushing air out or in the front pulling it in? I think I remember hearing that negative system pressure is good, so I was planning on putting it in the back.

Also, I'm a little concerned that putting it in the back will make it compete with my CPU fan for air. Not sure. I'm kindof a noob to the whole system building thing still...