Which gun is best?

Combat Machine M4 Raider Shorty w/Polymer RIS Airsoft Gun
Specifications:
Manufacturer: G&G
Model: M4 Raider Shorty
Muzzle Velocity: 315-330 FPS
Magazine Capacity: 450rds

D-Boy Full Metal MK16-L Airsoft Gun
Specifications:
Manufacturer: D-Boy
Gearbox: Version 2
Accuracy: 120 feet
Muzzle Velocity: 400+ FPS
Magazine Capacity: 300 Round High Cap

Combat Machine M16 Carbine Airsoft Gun
Specifications:
Manufacturer: Combat Machine
Gearbox Type: Type 2
Accuracy: 120 ft
Muzzle Velocity: 320-330FPS
Magazine Capacity: 450 rounds


These 3 guns are the ones i am most interested in..
1) whats the difference between the short and normal barrel for the first gun?
2) Which gun is best for its price?
3) What upgrades can i get for these guns?

Thanks I appreciate everyone who can give their opinion.

In google you should search for

"what does tokyo marui compatible mean?"

"______________(gun name) review" Just look at the adult ones

"Do airsoft scars have good internals?"

"Does airsoft inner barrel length affect accuracy?"

You should go by PB Matrix or your local airsoft shop and hold each one so you can see how they feel to you and ask questions at the shop. I believe the G&G/Combat Machine (same manufacturer) make a better, more solid product than the DBoys (I owned both brands) but if you like the MK16/SCAR, then you should really look at them up close so you can see how confortable they are to you. Also, check out the JG brand M4 and G36 which are also nice. Good luck.