Best sub for music,

My approach with subs has always been "keep it simple".  I start with one and place it, walking the tightrope of performance vs permissible location. 

I throw on some bass heavy tracks and query A) Does it sound good? B) Can I locate the sub? If the answers are yes and no respectively, I leave it there. 

IMHO an unfortunate symptom of audiophilia is the need to endlessly complicate everything. 

I can’t add much more expertise than MC and Atmosphere, but only my personal experience. MC is correct that more subs even out the bass nodes. Atmosphere is correct that larger cones mean less movement and a smoother response. I have a small sealed REL for a small room that works well with my stand mount Von Schweikert VR-1s. I have two Hsu subs that work well for my music room with HT. The idea that you don’t need subs is folly. Music and its harmonics go below 20 Hz. That’s the goal. I think it’s better to go with two or more subs properly positioned (see the Harmon white papers) is better than the best single sub. I recommend setting your highest budget and starting with two subs of good quality, position them properly and tune them to your system. Reach for sub 20 Hz at a reasonable level and add subs when you can. One expensive sub is not better than two subs of lesser “quality” for the same price if properly positioned. It takes time and effort. Ideally you won’t even know the subs are there, until you turn them off. Best of luck. Play on!

I would totally go for 18" JBL subs. Four, to be precise. Or five. The more the better.

For once, I actually agree with millercarbon.  My subs are positioned to be and time aligned with my mains.  However, as I often state, THERE IS NO "BEST" anything.  It is all way too subjective.

I repeat:  There is no best anything. There is no best car, quarterback, tennis player, nor especially, no best speaker or amp.