Different brands have different strength.
I am a "out of the box" guy, my experience is:
Tokyo Marui Next Generation - full metal body, have "blow back" action, good range, reasonable rate of fire, very reliable. Overall quality is very good. Power is on the lower side but it is good for me.
G&G Top Tech or Max Level guns - internals are already upgraded and well tuned. Excellent external finishing. If you are a strong guy, their M14 is a great choice with good accuracy.