I have owned both (still have Scorpion). I am a die hard AR guy having built my first one in the early 80s. Despite this heavy bias, as a 9mm platform in an SBR configuration and suppressed, I would go Scorpion. IMHO opinion it shoulders and shoots much better than my old integrally suppressed 9mm AR. The action seems smoother and has less felt recoil.
As far as blowback in the face there is no comparison, the Scorpion wins easily. A poster above pointed out some downsides with the Scorpuon. Fortunately most if not all either are or will be in the past. Stocks are hard to get because of the pent up demand which has decidedly eased up. In addition to the factory CZ stock, there are now several aftermarket options.
The compliance issue (if its even real) will be a thing of the past in the next few months. In addition to the CZ compliance kits, there are now a hand full of companies making pistol grips, muzzle devices, stocks, followers and base plates and triggers etc. Speaking of triggers, there is a spring kit available that greatly improves the trigger. In addition, several companies are said to be making drop in triggers.
CZ custom makes a barrel in 1/2-28 and any competent gunsmith can rethread the stock barrel in 1/2-28 and leave enough 18x1mm threads for the barrel nut. CZ has also announced that the 2016 production units for the US will have 1/2-28 standard as well as the option of FDE.
As far as the US Market is concerned, the platform is young and many enterprising companies will jump in with aftermarket offerings. As stated above, the ergonomics are terrible as a pistol without a brace. If you buy plan to SBR. If you do SBR, by the time you're approved all of the downsides will be gone.