If you want a bit of old school AEG that can be a beast for CQB games out of the box, you can always opt for the Tokyo Marui MP5K High Cycle AEG. It has a high rate of fire, at around 25 BBs per second and powered by an 8.4v NiMH stock battery. It also has a top rail for mounting a reflex sight for better aiming. Mach Sakai goes over it in this video review.