A good sub is a good sub, but I believe that music demands more of a sub in the sense that CERTAIN flaws in a sub may be more apparent when listening to music.
So given a two subs, one that is +/- 2dB and distortionless to 32Hz, and another that reaches down to 20Hz, but has a 3dB peak at 25Hz, and a slight dip at 80Hz...
So, neither sub is perfect, but each sub makes different compromises in their design.
I would say the first sub would sound better than than second sub with musical material, but the second sub might sound more impressive with movies. The second sub compromises a bit of FR linearity for more impact, but the first sub does everything right for 99.99% of music.
So if I were picking a sub for movies, I'd more likely take the compromises made by the second sub and choose it for my home theater.
I already know which sub *I* would buy with unlimited budget (one contender would be the Wilson Watchdog sub...man that thing rocks with music AND movies, utterly accurate with music)
A TRULY good sub would be equally good for both music and movies, but 99% of subs that you and I would spend our money on make SOME KIND of COMPROMISE. What kind of compromise do you want to live with?