a single 15 can beat two 12s. sub type, build, power. You have to think of the linear travel of the sub, the T/S ect.
Since that's your type of music I would recommend a single 15(15s typically have a lower FS) with a low FS and a high xmax. I would look into TC sounds subs. Those usually fit the bit for loud n low with good SQ. Whats your power range? Price, space confinement?