Firstly, it is important to note that subwoofers are engineered to perform best in one or the other, not both. So, you can't typically take a sub engineered for a sealed enclosure and expect it to be able to handle being installed in a ported box. Also note that the box must be "tuned" to the subwoofer as well. You can't just create a box of random dimensions and expect the subwoofer to play at its best. With all that being said, it is a personal preference. Ported boxes are inherintly louder and less controlled. If you are looking for the smoothest, most realistic representation of the original music, sealed enclosures work best. That is not to discount a perfectly engineered ported subwoofer system. I am speaking in general terms. There are some very superior subwoofers built to perform excellently in a ported enclosure, but you get what you pay for.