Interesting discussion going on here.
However, in true AVSforum fashion, "best" is appearing to be defined by the most headroom and extension at any given price point, with a complete disregard to timbre, decay/ringing, linear excursion (okay, maybe not that one), amplifier/DSP feature set, quality of enclosure finishes, etc.
There is a LOT more to a quality subwoofer than just blasting 20hz sine waves at levels that will piss off your neighbors.
Especially timbre, and how a subwoofer integrates with mains is something not discussed very much at AVS, because it's hard to correlate specs to timbral differences (extended range waterfall decay is the closest we can predict from). A lot of guys around here will just spout the whole "every sub operating within the same distortion will sound the same" nonsense. My advice to them is to listen to more subwoofers in their room at LOW volumes and then report back. If they still cant hear a difference, perhaps its time to enjoy a new hobby.
Having said that, my list would look similar to others, except I would give more value to finishes and feature sets as my subs are in a family room. You guys back east with basements (who I am jealous of, BTW) can put any ugly refrigerator sized, sprayed with bed liner behemoth anywhere you want and it doesn't matter, instead leaving you to enjoy the value of performance alone.
I also bring up feature sets because I believe there is great value to having a driver, enclosure, amplifier, and DSP/EQ in one box. If it's well engineered, that is TOUGH to do piecing it together from nonconforming parts yourself and having the finished product be nearly as balanced. Take the SB16 Ultra for example, which I own a pair of. With the dual discount and returning customer discount, factory direct is about $1800 apiece. I would challenge anyone to build that for $1800. The driver is a serious one, strong amp, parametric EQ, Bluetooth connected, beautifully finished and radiused cabinet, and here's the best part, a 5 YEAR WARRANTY. It's easy to say you can get more SPL out of an off the shelf 18, a sheet of plywood, a hot glue gun, and a crappy pro amp, but when you really look at a unit like the SB16....boy, that would be hard to do for that little money. The DSP stuff would end up doing you in. There's a lot of R&D there.