I can't think of anything inhernently better about any of those subs mentioned outside of the Dayton HO that makes them inherently better for SQ. that being said, I've never heard the Tantric LD series, so I can't speak on it's actual performance, just basic parts used an their general abilities. Morel and most "boutique" car audio brands dont' impress me much, so that'd be bottom of my list out of those tbh. The dayton Ho is a very well built driver at a great price point, it'd be top of my list out of those.
IDQ's and W6's can both sound decent and use pretty normal technology in their speaker. I'd assume the LD would fit right in, in that group, should be in good company. The flatylne is also in this group and can def be in a winning install. What subwoofer you use in a pure SQ install is almost of no consequence although some subs are inherently better than others at certain things and if you install gets exotic there are often different choices, but to chalk something up as "SQ" or not "SQ" can be hard and really comes down to an install by install basis.
Some subs have inherently low distortion due to better designed motors. Shorting rings lower inductance, like the Dayton HO uses, allows subs to integrate smoothly with nice response up to the crossover point where it meets the midbass. In a car where subs are behind you this can be crucial and most SQ subs in car audio dont' use them. Yes you can still make it work, if the sub has a small coil the rings may not be needed and some motor/coil designs are better than others in this regard. Then their are BL linear topologies like LMS and XBL^2. Drivers like that tend to sound very good even when the cone is moving very far. Again very few drivers use those, and you can have a good sub without them. You may need a bit more cone area, or a need to port the driver to reduce excursion, but again there are always work arounds. That's why I like the Dayton HO, it uses shorting rings, has a quiet suspension, decent xmax and powerhandling (it's underrated on the spec sheet a good bit) and the t/s lend it to smaller ported boxes to give a nice response in car. If your willing to use more cone area AE speakers makes an IB capable subwoofer that can give you good output, good low end and uses shorting rings. They also have their AV line coming back, it's a Dayton HO on steroids, if you want double xmax and powerhandling, howerver, at 799 it too is overpriced now, by a bit, at it's old price of 300ish years ago they were KILLER //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif At 500 I'd be more willing to reccomend them.
There are a few subs that use both rings and a linear motor.. The Illusion audio CXL uses xbl^2 and shorting rings, it's alsoat 1k.. A cheaper alternative is the SI BM MKIV for half price or a bit less than half has the same bells and whistles, shallow mount small sealed boxes only. If you wan to go BIG, the LMS ultra is beastly
Always depends what kind of space you have to work with and what response curve you want.
