Two subs will yeild a better response than a single sub, so I would go with two subs if possible. The Speedwoofer 12S will have a bit more low-frequency extension than the Hsu VTF-2 mk5, but the VTF-2 mk5 will have more mid-bass punch.
The VTF-TN1 has a very substantial performance advantage over either of the 12"s. Even two VTf-2 mk5s or two 12S subs would not equal the midbass output of a single VTF-TN1. The TN1 is a larger sub, but only in height. The 12" subs actually have equally large or even larger footprints, so they would take up a lot more floorspace. Two 12" subs would probably be sufficient for your situation, but two VTF-TN1s would be a hell of a lot of fun.