A supressor won't do anything to accuracy. The M16 would probably be a bit more accurate at range due to the longer barrel, as has been stated twice already.
Is the JG M16 RIS comparable to the G&G M16 RIS? And is the JG M4 S-system comparable to the G&G one?
G&G is probably better overall quality, though not by much. At least with G&G you have the metal upper reciever.
Keep in mind that all of those guns are too hot for indoor CQB play, and you'd have to downgrade the spring.
I should also ask: You are at least 18, right?