Ported box is going to be louder overall, sealed is for tighter, more controled bass more for SQ. Depends on what you're looking for out of a set-up, the subs you're going to be running and the amp powering them.
ported is more efficient, and thus louder at it's tuned frequency, but at the cost of more transient delay. It does increase power handling a bit, though, which can help.
Sealed will yield a flat response, and therefore more accurate without use of a 1/3 octave EQ to trim the response curve. Sealed will hit more deeply, as it doesn't roll off like a brick below the tuned frequency like a ported box, sealed does not require a subsonic filter to protect the sub, and sealed is faster. Sealed also requires less air space per speaker.
I'm a fan of sealed for SQ systems, but if this is for lots of bass, and for hiphop/rap and the like, I'd say go with ported, definitely. If you prefer very fast, tight response for things like detailed drum response low instrumental response in music like Jazz, Rock, or Classical/Baroque, go with sealed.