What subs do you think will pair up best?

Velodyne DD 18, Infinity Intermezzo 1.2s, and/or Def Tech SuperCube 1.

And please don't start with "It depends... "
Pair up to do what? Pair up with what? Pair up best...? It depends.
Do you mean pair up with another subwoofer or a particular speaker?

A pair of DD18's are great as well as a pair of JL Audio F113's. These were the two front runners when demoing. Extremely safe bet IMO!
It dep...whoops. Velodyne DD18, because it has so many adjustments and can be taylored to the room.
Like it's been already said, this is kind of an open-ended question. We need more specifics. So, of course it's going to depend. You got what you asked for! :)
Yes, they will. Honestly, you need to give us more information... pair up with what? And what are you going to use them for? Home theater, music, both? What is important to you? Very deep bass? Accurate bass?

This is kind of like asking which car is best? Well, the correct answer IS "it depends"... are you going to use the car on the track only? Are you moving 400 lbs of mulch? Do you have 5 kids? Are you driving only a handful of miles to and from work?
I like this newbie's username and now he's......

Anyway's, the JL or Velo will give very deep and very accurate bass. "It Depends"
JL Audio gets a lot of deserved attention, but I would suggest you look at the Paradigm Sub 1. It has 6 drivers and is very fast and flexible. It is an incredible Sub and comes with the Perfect Bass Kit which I feel is one of the most sophisticated of the bass EQ systems out there allowing adjustments up and down (most only bring levels down) and stems from the Anthem ARC development.