Don't think there's any more support at the front of an MP5 for the mechbox than with the M4. Version 2's are fine. Reinforced mechbox shell (a good one...not the crap clone stuff), 380-ish range, don't play in the cold and it'll last for a long, long time. In a TM mechbox...it's much the same, but I'd stay in the 350-ish range to take the sting out of it.
Lots of the pros/cons are covered already.
Fit the rifle to you. Some guys don't feel good behind an MP5. They find sighting impossible without a high optic mount (typically while using PB goggles). Some guys find the M4 too long for them, it'll hit the ground/etc...when they kneel going for a secondary.
Fit the rifle to where you're playing. If it's tight indoor CQB...the M4 is going to seem long. If you're not careful, you'll find your rifle sticking out around corners/through windows/etc...before you're ready to sight and shoot back. That and you'll find you're banging it into walls, doors, etc....
For outdoor games, the longer barrel helps a lot. Some guys will stick a long inner into an MP5 and hide it with a suppressor to get more accuracy at range.
Collasible stock MP5's are the pits for batteries. With a full stock MP5 you can run a big battery in the stock. Otherwise you'll be cursing dead batteries in the foregrip after a season of steady play. Anyways...with a full stock, the MP5 is not a huge amount smaller than a collasped M4...especially if it's a M4CQBR.
I find MP5 mags to be hard to store, both in a rig and in a dump pouch....they're long. Granted...my stuff is setup for M-series rifles.
I've had/build/worked on several of each. I much prefer the M4. I use it for both indoor and outdoor.
With the exception of CA/ICS MP5's...the M-series is easier to work on. "TM" style MP5's are not favourites to work on.
Metal rules. Here's what I'd get if I were to buy AEGs again and had to pick an "off the shelf" model.
- Classic Army
- CA MP5 full stock
- ICS MP5 full stock
I'd get a full M4A1 style and a CQB one. The mags and batteries would be interchangeable. The CQB would be set to indoor (sub 350) and the other to (380-390). The CQB would be the backup rifle for outdoor games...a pistol would be the backup for indoor games. One rig setup for both rifles. Rails and lights and stuff for the CQB. Light and lean for the M4 field rifle.
Anyways, best of luck.