It's a number of things that makes one better than another.
The total sum of the: efficiency, power handling, cone size and excursion goes a long ways...
Nothing beats a PA sub above 40hz. 4-8 PA-18's or 21's that each handle 1000watts at 99db/watt, is gonna break drywall/noses and bleed out ears and eyeballs.
Below 40hz usually the most massive sub wins. Just pure beef-ness.
The threshold of pain and ear damage threshold at 20hz is something like: 140-170db. So you can never really have TOO MUCH
people stop at around 8 18's as the SPL get's pretty crazy and diminishing returns kicks in hard at that point.
Usually, you can only be hit in the head with a frying pan so many times.
At 16 18's and 16kW+, the box design almost doesn't even matter anymore because it's just plain loud to matter how you have it thumping,
and unless you live in a cement underground bunker 1 mile away from the nearest person, then there is no practical way to bang it at max for more than a short period of time before cops fine you big money or just simply take your gear away and throw you in jail for a few days/weeks. (Which is pretty much the point where I'm at now.
You can only buy/have so many cones in a room until you/it looks like: hoarder or prepper or nuttybar (or a mix of all of them.)
But don't mind me, I'm just listening to bass while eating astronaut-icecream and survival-rations/ramen in my off-grid vault, Howard-Hughes-style