The 20's are going to sound tighter, mostly dew to the smaller enclosure. I have heard from a few people the 20's are easier to soundstage and have a much better presentation. Now of coarse they won't beat the 60's on the bass part, but with a sub it will not matter anyway. Also not that many...
I had an HSU VTF-2, a very solid performer. Deffinetly the better way to go. I just wanted to be sure you weren't getting a Paradigm PS series sub or something, because those are not worth the money. You may also consider looking into the SVS subs like the PB-10 NSD. It should go deeper than the...