I've only had the Vapor and 4.3, but from what I hear the 2k12 is really a happy medium between the two, without the real great advantage of either.
But I can say that the Vapors are the most comfortable shoe I've ever owned, period. They somehow hug the foot so well, and are low to the ground, which I really like.
I switched to the 4.3's because the Vapors are not very durable. The 4.3s feel fine, but nowhere near as comfy as the vapors. But the good news about the 4.3's is that they last much longer. I had a pair of 3.3's that lasted a long long time, and I can already see after a couple of weeks how much more durable the 4'3s are from the vapors.
So if you want a fast and just out of this world comfortable shoe, that you will have to replace more often, go with the Vapor.
If you want a long lasting shoe that really commands the court, but may feel a bit clunky, go with the Ballistics.
I miss my Vapors personally, but for a time at least, the cost to keep using them was too much.