It doesn't matter really. As long as the cabinet itself is ventilated adequately, you shouldn't have any problems.
Just get a couple of those big ass PC fans ala

Put em on the back and put a couple vents up front and you should be fine.
Plus the large fans move more air at slower RPM's so they're quieter.
(ok, I'm half kidding about that fan, it's over the top large, but a couple 6-8in ones should do the trick)