If you're really crazy about sq then i guess you could say the "sql" woofers sound better. Even then it doesnt matter so much how nice the woofer is. The box determines how good its going to sound. If you're still going for SQ while being loud you have to deal with tons of sometimes overwhelming vibrations and rattles. After a certain spl level deadener only does so much for rattles and vibrations.
Just like Srim said its install dependent. ive heard w7's that have sounded terrible, and ones that sound really good. I've used a variety of SQL and SPL woofers and honestly i cant hear much of an SQ difference between a quality SPL woofer in a quality ported box and any other SQL woofer in a real world daily driving environment. My btl running at about half of its mechanical limits sounds just as musically accurate as other setups sealed or ported. Most ported boxes sound like shit as they're prefab. Only so many people frequent forums like this or have the cash to shell out for a shop to do it right....even then some shops will still **** up a $500 box.
What i love about my btl is that i can turn it up just loud enough to blend nicely with the music and sound great, or turn it all the way up and abort babies in my front seat. Even at full tilt the bass is pretty **** crisp and clean. BTL, MT, 5200, dd9500, etc in a tuned for daily driving quality built ported box will sound just as great as virtually anything main stream, while completely shitting on them in the SPL aspect.
my old roomate has 2 low end round sony xplode 12's and a volfenhag 2ch amp in a prefab sealed box. Swap shop in miami installed it for him and it sounded like complete garbage. later he would get a new car and i was brought in to transfer the gear. I resealed all panal joints with glue, sealed the speaker wire terminal hole where the plastic terminal was loose for crying out loud. 2 tiny holes big enough for the wire did the trick. installed everything into the new car and properly tuned the amp (swap shop had that jacked out too). The SQ difference is like night and day. I couldnt even believe how good they sounded for 4 year old sony's off a Vhog amp.
IMO if you have the budget get a single spl woofer, do the install right, and enjoy the benefits of great sound for a loud daily driver with the potential to get insane loud.