You will want subs that have similar performance and designs. Like, if you get ported subs, get subs that have similar tuning frequencies and roughly similar output capabilities. For example, if you get a VTF-3 mk2, you can match it with another ported 12" that has tuning frequencies in low 20 Hz range or high teens. almost any of
these would make a good match for the VTF-3 mk2, except perhaps for the SVS SB-2000 since it is a sealed design.
If you decide on a sealed sub like the B&W, match it with other sealed subs of roughly the same performance. The SB-2000 would probably make a good companion for the B&W sub, since I am guessing it will have similar performance characteristics.