slightly old post but it might still be useful.
i dont mean to throw a wrench in the mix but i think the JG m4s make a good gun. i have a jg m4 s-system and it hasnt stopped running for over a year now and it shoots true. i also know a few other people that have them and the same is true. on the other hand i did hear that the mp5s are not quite up to par with the m4s. that seems to hold true with all the manufactures though.
so there it is, my .02