I agree with Dan, for the most part.
Zpacks' hybrid is 50D nylon, HMG's is a bit heavier, maybe 100D, plus the 1.4 cuben inner.
VX-21 is 210D nylon plus a 50D nylon inner.
Tear resistance goes to the hybrid stuff. High density spectra is far better than the X threads in the x-pac. VX-21 seems more abrasion resistant in my use. Waterproofing is a wash, as both are excellent.
X-pac is half the price and about twice the weight. I think the cuben stuff is better for most applications, especially if you can get a heavier weight than Zpacks' offering. With that said, good luck finding a source. Both, IMO, are better than 210D Dyneema X, which is not so waterproof, while being slightly more tear resistant than VX-21 but not as abrasion resistant.