ported is louder, and is you listen to mostly rap, trust us, go ported.
if you have max 3cubs to work with i'm sure you can find something in 2.5cubs ported and still fit. if you build the box right you probably wont notice any SQ loss from sealed to ported. if the box isnt well built, itll sound like shit either way.
i'm sure there's plenty of 15's out there that'll do well in 2.5cubs ported and tuned low with 1kw - 1.5kw
iirc mobieus (sp?) is in lakeland and makes solid boxes. hit him up
there's a guy in titusville thats does smal boxes for cheap. ls2powrcoat(sp?) or something, cant recall his exact user name spelling off the top of my head. but get in touch with him and make a drive.