It really depends on the model of subwoofer you're using. Different subs like different kinds of boxes.
With your W3s, a sealed box is your fastest ticket to quality bass. The sound will be nice, tight, and snappy. Ported boxes put out a lot more low frequency sound (aka BOOM), and the sound can be a bit sloppier than that from a sealed box. Ported CAN sound good, if the box is designed properly and built perfectly, however.