Exhaust Or Intake

I would say to have bottom as intake so you have a good intake and exhaust of air instead of having both blowing out, causing air to be sucked in through all the little gaps in the panels and front of your case.

Best thing to do if you're looking for the best temps possible is to get a copy of Aida64 (or something similar) that shows temps of all your components and write them down. Then swap the fan around and measure temps again. I wouldn't be surprised if the difference was pretty small - but might be worth doing anyway.

ace

Hands down that should be an exhaust port. The psu doesn't pull enough hot air out to make it effective. There are vents at the front so cool air is drawn in and hot air exhausted out the back.

Leave that setup so that you will have proper airflow

Exhaust. Your fans are working against each other in your current config. Airflow is disrupted and you have a bunch of hot air stuck in the case. You could always cut the side panel near the front of the case and put in a fan. Sort of like the NZXT Phantom.

My instincts say: both should exhaust. That being said, the only way to truly find out is so test. You only have two possible setups so that wouldn't be too hard to test. From an awesome article I read, which I can't find at the moment, tested multiple setups. I wish I could just link to the article, but one thing they did not expect was that having only an exhaust out the back scored very high, second place if my memory serves. The basic jist of the article was to go for good flow over many fans. One of the back fans blowing in, and the PSU blowing out seems like it would disturb the airflow more than help it.