MP5s are great. They're compact, especially with the collapsing/folding stocks, lightweight, ergonomic, etc. I have two Maruis, with an upgraded barrel and hop rubber they're pretty accurate to 40m, maybe a little more. They're well below the power limit but they're fine.
Another advantage is with mid-caps you get a similar ammo capacity to others, but magazines are half the size. (At least comparing Marui 416 to MP5.)