With a sub, quality is the most important thing. If it can go low, but is sloppy, it is not a sub that I want. If it goes loud, but sloppy, that is also a sub I do not want.
A good sub is one that does what it is designed to do, very well. A sub designed to go low should do so cleanly. A sub that is designed to go loud, should do so cleanly.
Pat