If you were deciding between the VTF-3MK3 & the new PB12NSD then you would have a very similar comparison. It would be probably slightly better to get the new PB12NSD over the VTF3/3. But im pretty sure the VTF3/3 will be abetter choice over the older NSD/2.
All i can vouch for is the HSU since ive heard it numerous times. I know you wouldnt regret getting one then maybe saving to get a second down the road!!
But maybe someone can chime in that has direct experience with the NSD/2 version.
Its hard though to compare subs unless you hear them sidebyside in the same room set to the same level.
Well at least you know that either of the 2 aregonna be a good sub.