well
you gotta tell us why you would want the gun.
If not,
In any case, I would say get the MK5.
Its an AEG, and its a CQB gun. Perfect.
Shotguns the bbs don't fly to far, so a MK5 would definetly increase accuracy.
Also the FPS wouldn't be as high as a MK5, so definetly,
THE MP5