I don't know what model speakers you have, but speaking from popular experience, Fosgates are better than Jensens, HOWEVER, I used to have a Jensen 12" DVC sub in a sealed enclosure in my car, and it was great. I liked it much better than my friend's fosgate 12" in a bandpass box.
I personally don't like bandpass boxes, as I think they tend to sound really sloppy and don't hit very well. As was said, for loose bass, they are good, but if you like rock, you want tight bass, and you can't beat a properly tuned ported box. The ported box allows for the same sound levels as a sealed box at lower power levels, thereby decreasing the amount of work the sub needs to do and decreasing the chance of damage to the sub or the amp.
If I were you, I would plug both into an amp and listen to the quality. See which one you like better. Also, what kind of box are the fosgates in? Sealed? Ported? Bandpass? If the fosgates are in a sealed or ported box, I would personally go with them, but if they are in a bandpass box, I would say to hell with the whole system and custom build a sealed or ported box.
Hope this helps!
JR