Who makes the best subwoofer for music? REL or JL AUDIO? REL uses High level, JL AUDIO low level with EQ. Which will be better for music. 
SVS is out. They are nothing but a big boom box. REL or JL AUDIO are the only consideration. 
I hav Jl audio,  rel  and M&k subs in my systems . All pairs.
IMO the sub choice  depend on the speakers you are matching them with . I use my Jl Gotham’s v2 pair with my magico M3 integrated with a cr-1 crossover and the integration and blend is seem less . The rel s812 pair  I use with my Charney horns using high level inputs . Good integration. Without an adjustable phase I feel  the integration is very good but not perfect . The ease of set up though is beyond compare .
 Took me with the help of bass guru Barry the Sounddoctor months the get the Gotham’s tuned in to perfection to the room with thr m3 . The Rels I could do it in an evening. They  sounded decent just plugged in  lol.
The M&k x12 pair I use in my home theater . Thundering sound effects . Set up using Dirac.
Each sub IMO is a diff beast . To compliment full range accurate speakers Jl audio,  if you take the effort will win. For just adding bass to a limited range speakers with ease rel would win.  Purely my experience. I have been a rel faithful from their st series . 
I have owned dual SVS SB15 and SB16 Ultras, HSU, JL Audio, Martin Logan Depth and REL subwoofers. I prefer the REL G1 mkII over every other subwoofer that I've owned. JL Audio subwoofers hit harder, but to my ears, in my room/system, no other subwoofer improved everything across the audio spectrum like REL. You can't hear my G1s when they're on, but turn them off while music is playing and I just shake my head.
I just switched from my Martin Logan Force subs and picked up 2 REL subs after demoing REL and JL Audio.  Extremely happy with the upgrade.
My JL crapped out. Been meaning to send in the amp to fix for $400 but haven’t gotten around to it. I hear it was a round of bad caps in the 1st couple years models.