If you can really only have floor space for one, or two, then Tekton 4-10 is the way to go. Get two.
And just to be clear this is not to have two times or four times as much bass. The reason, which you will find clearly explained all over the place if you look, is every sub no matter what or where you put it generates peaks and nulls. Using more subs in different locations creates more peaks and nulls in more places. But having four lets you run each one at a lower level. The result is they all sum together into much smoother, deeper and more powerful bass than you can get any other way.