I used to have a STF2, that was a great sub. From the ones you listed, I would go with a VTF1, and run that sucker in max output mode, I think that thing would have a lot of punch. Emotiva has some nice looking budget subs on sale at the moment, but even between them and the VTF1, I would go with the VTF1, I think that would have a bit more impact.
There is a lot of praise for the BIC Acoustech PL-200, and you can get that for under 300 if you look in the right places.