Had a Fi Q12 myself. Not terrible, but I wouldn't recommend it for SQ at all. WAY overrated sound, IMO. Though it does get impressively loud.
Some subs with good SQ in no particular order:
Peerless XLS/XXLS
CDT QES-*
Focal anything
Dynaudio anything
Morel anything
JL W6 (and W7 isn't bad)
Exodus Shiva/Tempest X[2]
Acoustic Elegance / Lambda / Stryke anything
CSS SDX* (10"... 15" is supposed to be coming back)
Stereo Integrity Mag / BM (hard to find, though there may eventually be more made... keeps getting delayed)
Dayton Reference
JBL WGTi isn't bad (I'd call it a slightly better version of a JL W7)
TC Sounds Epic (and similar - they've had about a million variants over the years)
TC Sounds LMS 5400/Ultra - Relatively high inductance but the LMS technology does help keep the BL curve pretty nice
IA Flatlyne (underhung voice coil, which is good... but I won't support that company)
IDQ (similar to Dayton Reference, actually... IDMAX is decent as well)
Arc Audio Flatline = IDMax with a flat cone
Arc Audio ARC = ID (or was it IDQ..?) - ID is okay as well. Not sure I would call it "SQ" but I wouldn't say it's far off.
Aurasound NS-10 or higher (i.e. larger; they use the NS marker for midbass/midrange speakers as well and those vary in quality; some are crappy. The large woofers/subwoofers rock.)
etc...