Depends on your budget and trunk size. If money isn't a problem, then JL 12W7 in HO box will do wonders. If that is a bit too high, RE X.X.X. in well designed ported box will be just as good at a much lower price. I like JL's warranty, they will replace the sub with a new one for 2 years.
XBL^2 isn't really to blame, it's the really high mass paper cones they use on the subs, and the suspension components. The soft parts of the W7 is what makes it a better sub IMO. The BL curve of the W7 is also better than the Brahma or XXX, especially the 12W7 and 13W7.