Hi,
I have both. I personally prefer the Mach V, but I can't really quantify why.
It feels narrower, and looks like it has less bits picking out around the backplate. It generally feels more stable underwater.
That being said, my gf appears to have taken posession of the Mach V, and when I dive with a single tank, it's almost always with the Hog wing, and I haven't felt the need to get a second Mach V.
Both seem to work fine without an STA, although I normally use a mini-STA on the HOG so it's easier to switch between singles and doubles.
Cheers,
Pasc