If I could only pick one, I'd choose the Sig MPX Copperhead. Such a soft shooter. With only a 3.5 inch barrel, this shoots 1 inch groups at 100 yards. Because of the piston system, it shoots like a 22 with power of 9mm.
The CZ Scorpion micro is accurate as well, but that huge direct blowback bolt kicks the shoulder harder.
I've shot full auto MP5s and I have to say that the Sig MPX Copperhead shoots even softer. Sig really mastered the 9mm PDW.
Both great guns, but if money is not an issue, get the Sig MPX Copperhead. If money is an issue, get the CZ Scorpion Micro.