From a pure technical side, the Kraken is probably better. V3 are more sturdy, and MP5 have a tendency to get selector problems. But there's already a bunch of thread that can be found easily about it!
And playing "out in public" as in a backyard is dangerous. There's probably soccer moms around (that would call the police if they see anything remotely looking like a gun), many people without proper eye protection, etc.