My G&G CM16 has outlasted both my E&C301 and Echo1 as far as stock issues.
E&C lasted 1 games and burnt out.
Echo1 lasted two games and burnt out.
CM16, no jams, misfeeds, battery issues. Nothing. Solid, out of the box all stock, indoor and outdoor.
That being said, I also have an Ares G36c that I love more.(Even with all its magazine issues) But as far as M4's go, its easier on the field as more people run them so magazine compatibility issues are slim to none.
Next M4 will be either ICS or VFC.
Please note, This is my first year playing and only basing my opinions off of what I've played with.
VFC/Umarex HK416 - Daytona G36c
Ares G36c - Echo1 ST6
Tokyo Marui HK45 - WE Glock 17 - WE Sig Sauer P226