Of the two, my choice would undoubtedly be the Hsu. However, it's a very close race.
Roger Kanno, a reviewer for Home Theater & Sound, found the following while reviewing the bigger brother of the Mirage Omni S10/Energy S10.3, the Omni S12... "Although the Mirage was very agile, the Hsu [the VTF-3 Mk II - which is comparable to the Omni S12] is even tighter and more controlled. The heartbeats from Dr. Chesky’s 5.1 Surround Show sounded cleaner through the Hsu, though there didn’t seem to be much of a difference in output levels (except with the 20Hz tone, where the Hsu seemed slightly louder). At reference levels, which most people find far too loud, the Hsu was clearly able to play louder with less distortion than the Mirage; at normal listening levels, the differences were almost indistinguishable."
However, he also went on to state that "In fact, in my day-to-day listening (which some would still consider to be very loud), the Omni S12 consistently surprised me by keeping pace with the Hsu VTF-3 Mk II. If you don’t want a big, unwieldy subwoofer in your living room, the Omni S12 will provide as much bass performance as most people will ever need."
So the differences are not huge. You'd probably be happy either way.