Take the following with a grain of salt since it's just the (quality checked) aggregation of what I read over the last year or two.
the SVS NSD is considered to be a great value for movie use, but maybe not so much for music. The downsides for music (all hotly debated but they seem to match my limited experience) are (a) relatively more output comes from the port & cabinet so rapid bass not as "tight" (doesn't cut off as fast), and (b) frequency response not quite as flat (haven't looked at charts so less sure about this one).
I have an SVS PC Plus (cylinder, not box, bought before the high end Axiom subs came out) and am happy with it - if I were buying now I would probably try an EP500 and would expect to be happier in some ways (flatter frequency response, probably better with music, hard to overdrive) and less happy in other ways (probably can't produce quite as much output as the PB Plus).
I don't know anything about the SB12 other than that it presumably is a sealed box sub so peak output will probably be lower unless it has a huge honkin' amp (it might). Should be good for music though.
If you want a very crude ranking loaded with all kinds of stereotypes (but probably not wrong), based on the prices above, I would suggest something like :
Best value for movies - SVS NSD
Similar to NSD for movies, better for music - EP350, SB Plus
EP500 and PB Plus would both be a step up, with EP500 maybe a bit better for music and PB Plus maybe a bit better for movies (this is getting even more tenuous).
Remember this is free advice and worth every penny
EDIT - I should mention that I have never been particularly happy playing music with a sub and tend to listen with the sub switched off. Not sure if that is because I don't have the right sub yet, because I need to tinker more with placement + crossover settings, or if my ears are just used to the response curve I get without a sub.
FWIW I'm running :
HT system - M60s, VP180, QS8s plus M2s waiting to be hooked up as rear surrounds
Music system - M40s (discontinued 2 way, like M3 but tower cabinet)
