as far as i could remember from previous discussion, the smallest one should be the best for music since it is louder on higher frequency. the bigger ones could go lower, but wont be as loud as the smallest one on frequency above 32hz ( could be wrong here ).
I have demoed the 25-31 and 20-39 and I detect no difference in tightness and accuracy for music. I rate both a "7" on a 1 to 10. Above average for music. The 25-31 was the old driver. 20-39 was the new driver.
The best subwoofer for music is going to depend on so many variables...its tough to point to one model and say *thats the one that is going to sound best to you(if you could audition 100 different subs)*. The room size and layout. The location of the sub,and key seating. The calibration of the sub,including making sure the phase is optimized. The type of music,the volume levels you generally use...and perhaps most importantly...simple personal preference/bias.
Any well designed sub(hsu,svs,paradigm,vel,mk,ect)should perform very well on music IF you can optimize the variables I mentioned above.
It is important to consider a subwoofer that will extend