We had our HT meet here today with a few AVS members. I'll just say that after comparing one ULS-15 to one VFT-15H, which including trying both subs in the same spot, and moving them around, there really was never much doubt regarding which sub was preferred.
I'm not going to speak for others who were here, but from my standpoint the ULS-15 was seriously lacking in bass impact. So much so that we all found it rather surprising and confusing. We double checked the settings to make sure it was set correctly etc. Honestly, even without comparing the ULS-15 to the VTF-15H, I would have been disappointed in the ULS-15. Although we could clearly see the cone moving, I personally wouldn't rule out the possibility that there is a problem with my unit.
The VTF-15h performed extremely well in my opinion...both open and plugged. In sealed mode, I thought the bass was a bit tighter, but there was not enough of a difference in my opinion to justify losing some of the impact of running in ported mode.
In any event, I'm going to return the ULS-15 and go with two of the VTF-15h's. Thanks a ton to the guys at HSU for allowing me to try both subs out to see which I preferred!