To be honest, I think you will be happy either way.
Ported will definitely be louder, while sealed will yield better sq and tighter bass
However, a low ported box (such as 32 hz) will still have good sq while getting impressively loud
On the other hand, I can't imagien that dual sealed 12s would be quiet either...
If you have the space for ported, I would reccomend a low ported box built to your subs specifications. If space is an issue, go with a correctly sized sealed box.
Either way, I am sure you will be happy.