Best sub for music,

multiple subs and how you arrange them, personally I like the way my Martin Logan subs integrate with my various systems 

There is no best anything.

I have a single REL S5 mated to my Klipsch Cornwall IV speakers.  The Cornwalls don't need much supplementation at the bottom end but I think the S5 integrates perfectly with them.   My S5 is set to roll off at the top end at about 32.5Hz.  All my audiophile friends that have listened to my system complement how well the S5 integrates with the CW IVs.  Signal Cable makes a great Speakon connector subwoofer cable that I use to attach to my power amp's binding posts.

There is no best anything.

Ah, com'on? Off the top of my head: 
Flint's ribs.

A Fenton's Black & Tan sunday.

The 1982 South swell. 

Jimi! 

@mijostyn --

I do not know where this differentiation between home theater subwoofers and HiFi subwoofers came from. There are good subwoofers and bad subwoofers. Perhaps home theater people tend to buy bad subwoofers. Good subwoofers will do anything. They are even better at doing theater than bad subwoofers.

Most commercial subwoofers are not even fit for home theater duty. ...

Much in agreement here.

It is very hard to make an enclosure that works at a reasonable price not to mention terrible cross over strategies. Play anything with a lot of bass and put your hand on your subwoofer. That vibration and shaking is distortion. Ideally you should be able to put your hand on it and feel absolutely nothing. I made 200 lb enclosures out of solid surface material and I could still feel some vibration. Next versions will be better.

Front loaded horns, tapped horns and (other) high order bandpass subs lend themselves better to enclosure rigidity due to the horn paths and chamber innards inherent to their construction. That said adding density by factor 2 or more to such cabs that easily take up 20 cf. of volume, and already weigh in at +200 lbs, is highly impractical and would seem to miss the forest for the trees; I’d much prefer their virtues of higher efficiency, better cone to air coupling and bigger effective air radiation area at a lesser package density than a smaller, less efficient and relatively heavier ditto.

Stay away from ported subwoofers. Subwoofers have to move a lot of air and it is very hard to avoid port noise. It is better to stick with sealed designs and correct the frequency response with power and room control.

That’s an unfortunate generalization. Sealed designs are hideously inefficient, and power only gets you so far - unless you have an abundance of displacement. Moreover mechanical stress associated driver noise would be obvious due to it being direct radiating - this goes for all DR designs. Ported designs when tuned low (with prodigious venting area) and using large diameter higher efficiency pro drivers can lead to good results, and if port noise would be prevalent here I’d suspects SPL’s to be substantial. Front loaded and tapped horn subs suffer no horn path noise. Theoretically it’s not impossible, but you’d have likely bought the farm by them - certainly structural integrity of your housing. Tapped horns have the driver "exposed" at the mouth area (re: mechanical driver sound issues), but with excursion minima at the tune are even better loaded compared to FLH’s, and so distortion levels are lower due to less cone movement at all but at the absolute limit of their capabilities (hence the prevailing logic of headroom).

Regardless of the size of the room the minimum size is two 12" drivers or four 10" drivers. Bigger and more is always better. The less work any single driver has to do the lower will be the distortion. Making sub bass requires long excursions which take the suspension out of it’s linear operating range. Bigger and multiple drivers do not have to move as far.

Front loaded horns and tapped horns (and other high order BP designs) are force multipliers; a 15" driver like the one used in my tapped horns is the equivalent of some two 18" direct radiating drivers - both due to the horn loading of the front wave of the driver, as well as the taking advantage of its summed output from the back wave - although they present bass quite differently to one another and hereby making comparisons a bit tricky in this regard. When you factor in high efficiency, large effective air radiation area and excellent loading of the driver (with proper motor force and other criteria met) that has the cabinet/horn do the heavy lifting, it equates into effortlessness in reproduction like few others.