<font color='#000000'>To a very great extent, it depends on what you are trying to accomplish. I take it from your comments that you plan to build yourself. Suggest you look into transmission-line enclosures. Harder to build, but worth the effort. For a simpler enclosure I agree with the previous advice, in that I'd go with a sealed (acoustic suspension) system over a ported system *in most cases.* However, if you just want to add some room shake to an HT setup and don't have a big amplifier to drive the sub, a ported box can do the task. IMHO, bandpass subs aren't really useful for home use, though they might be ok if you only use them over a very narrow bandwidth (which is all they can cover anyway).
Sealed box is the easiest compromise. Transmission lines are an improvement, but are much harder to construct.
Hope this helps,
Chuck</font>