STF-2 should be great. If you have extra to spend, go ahead and do the STF-3. I'm 18x12x8 VTF-2 and it's plenty. You're only a little bigger. I'm only VTF cause there was no STF when I got mine. I don't know of anyone that actually uses the V part of the VTF, so get the STF.

And IMHO get Hsu, not SVS. I compared both and preferred the VTF. There's an old post on it somewhere on here.