negative pressure should be avoided unless stated by your 3rd party hsf. this is due to negative pressure setup unable to cool your hdd unless u install heat sink/fin for your hdd.

basic guidance:
front : in
side : in
top : out
rear : out

* though, this guidance is just basic, and may vary some times. it'l be better to apply btx style if you're running on a hot gc.

** however, make sure the air flow OUTSIDE your case is also good enough for the hot air to move away, to avoid the front fan to suck back the hot air from the rear (*rare occurance, recycling of air). and make sure room temperate is nice.