Basically, if you're a person who can control recoil very well, such as tapping and controlling bursts, the G36E holds maximum potential for players. The Mk-16 and M4A1 are for players who are more comfortable with spraying or does not wish to worry a lot about recoil.
Generally, if you say the G36E sucks, it's only your lack of putting it to good use thats holding you back.