It really all depends on what you are trying to achieve. Do you want SPL or Quality Bass .. also depends on what type of music you mostly listen too. A smaller sub will give you better kick bass then a larger one.
ex. If I were listening to pop music 2 small 8" would sound better then 1 12" but I would use the 1 12" over the 2 small 8's for hiphop.
I've had sealed and ported boxes (good quality MDF wood .. not flea market boxes). The boxes were made to the specs of the speaker for best results. I can tell you one thing thou .. sealed will sound louder if the trunk is open and your trying to show off. Ported is louder if the trunk is closed and the seats are folded down with windows open. Those are the big differences .. you might notice that in competitions as well.
-=[ BL/\DES ]=-
All it takes is one bad day to reduce the sanest man alive to lunacy. Thats how far the world is from where i am. just one bad day. - Unknown