8 years LE, never a member of our agencies full time team, several years doing part time tac work while on patrol.

So long as your shorty M4's run well, and you guys have appropriate ammunition for them (not green tip, or other "ball" ammo) I'd go with them if I can fit a long gun into the situation. Getting suppressors that actually suppress would be high on my wish list for those M4's. On the off chance you have reliability issues with your rifles, or are required to run ball ammo, I'd personally choose the MP5. Reliability is paramount, and depending on the FMJ ammo you're stuck with it may fail to function properly somewhere past 25-50 yds. A good hot 9mm round will of course out reach this.

The MP5 is a heck of a subgun, but still a subgun. For the SD's I can see using it for when you really need to be quiet, or a few other specialist situations.

So overall if you've got good 5.56 ammo, and the rifles run, that'd be my choice.

-Jenrick