I should put one qualifier on that statement: the subwoofer's extension will make a difference here. That is one thing that you can hear from A/B testing. Certain brands like SVS and Hsu tend to make deeper digging subs, and that difference is audible. However that is more a quantitative difference than qualitative.
As for other parameters that people use to conclude subwoofer A is better than subwoofer B, one is dynamic range, ie., sub A can get louder than sub B. Again though, that is quantitative.
A lot of people will also just assume that since subwoofer A is more expensive, it will be better than subwoofer B, and since our expectations influence our perception, that is what they experience, regardless of what is actually heard. It's the same phenomena that leads people to believe their aftermarket power cable improved their system's sound.
Certainly if you compare subwoofers from A/B switching in-room, you will favor the sub in the location that acts more benignly with room modes. The only way to properly compare subwoofer's intrinsic sound is either outdoors or in a room so large that it doesn't activate any acoustic modes (A football stadium sized room might work).