What is it you're saying? That the MPX will be prettier with a suppressor than the EVO or is it something in the design like the MPX is a more familure layout (AR type controls) or that the MPX will make a more efficient suppressed ... exactly what are you getting at?
By attractive I meant appealing from an end user perspective, not its aesthetics. The CZ is a blow back gun. Blow back guns tend to have heavier bolts and thus are less flat shooting (muzzle rise during strings of fire, not external ballistics). For shooting suppressed the blow back guns typically have some disadvantages. First they tend to be louder with more noise out of the ejection port. Second you tend to get more gase and gunk coming out of the ejection port.
If you have shot say an MP5 and an 9x19 AR you will know what I am talking about.
The sig's layout and controls are arguably better as well. The AR charging handle is one control I think they could have done without keeping but oh well. The Sig purportedly using various AR parts is nice. I haven't researched it fully but it seems that one can drop an AR trigger in.
The CZ is also a much cheaper gun and will be less expensive to SBR in the long run, once the 922r compliance kit comes out that is.
What is the price of the compliance kit? I think its is impossible to make that assertion without knowing what it costs. I would imagine that out the door cost on a completely set up CZ will likely be cheaper than on the Sig. With mags costing between $30-50 more for the Sig that alone makes a huge difference if one buys a reasonable number of mags (I like ten at a minimum).
I can't really see buying either gun at this point. The sig is unproven and sig may well make changes a la rumors with the MCX. see
http://www.m4carbine.net/showthread.php?170320-The-Sig-MCX-2015-s-quot-ACR-quot
I'll wait on the sig and see what comes of it. They managed to screw up the proven Sig 55X series after all. I also am still hoping for them to have a version with the keymod hand guard.
As for the CZ, real deal CZ Scorpions are a proven design. However, the only reason to get one is to make an SBR. No compliance kit means I wont be making one yet. Some argue for getting the gun and getting the form in since one will have to wait on the ATF. That makes sense in some ways. However, the forth coming compliance kit is a big unknown. It seems no one knows what it will cost, what parts will be replaced, or really much of anything about it. Prices are still falling and mags are still rare. For a pistol call SBR I can bide my time and wait.
The CZ may end up being the go to choice simply because it may be so much more cost effective than either the MPX or an MP5 clone.