I can't speak to the G&G 416 as I have never owned or handled one. I will say that G&G guns in general are of very good quality. I have had other models that had "demons" out of the box, but it is rare.
As for the DPMS M4 S-System, there are two versions, one made by A&K with a metal upper receiver and one made by JG with an all-plastic body. Internally, I like the JG better (better quality components). Velocity-wise, the JG guns tend to chrono a bit higher (usually in the 375-390 FPS range with .20gr BBs versus 360ish for the A&K). The A&K version does have the metal upper, which is very important to some people.
If you are planning to do some basic upgrades, I would opt for the A&K version. If you are planning on using it stock for quite a while, go with the JG version.
You can tell the two versions apart by the color of the receiver, straight black is the A&K, while the JG has a gray color to the receiver. Good luck and enjoy!