I have no idea of what walter duque is trying to say. Not sure if he is trying to push you towards the HSU or the Monolith. Without knowing the final room dimensions, any advice, anyone gives is just taking a stab. Given the three choices you listed (there are many, many more that could be in the list), I would choose the HSU VTF 15H MK2. My reasoning is simple.....If I'm going to go big, I will go with the biggest (respected) of the bunch.....especially when the biggest of the bunch has been reviewed as a great subwoofer. Now if your budget allowed for more, then I would say hey...wait, that dang Monolith 15 is a heck of a subwoofer. Notice, I didn't say the Monolith 12....well because it is good, but again it is almost "NEVER" compared against the HSU 15 incher's.
I'm going to suggest you wait until you buy the house. The listening room will decide what is best. Who knows, it could be small enough that one small subwoofer works, or could be so large that it takes two large subwoofers.
As has been said many times, buy as much subwoofer as you can afford for the first one....and then save up for its twin, if needed