With all the ACM brands out there, I'd definitely go with D-Boys.
Whatever you pick (I suggest a CQBR), have a local airsmith do some preventive maintenance. This includes complete take down of the gearbox, applying lube, and properly shimming the gears. Watch him do the work, so next time, you know what to do.
You'll probably want a tightbore barrel (Madbull), a new hopup unit (unless the D-Boys have been improved recently, Systemas are pretty good), and a new hopup rubber and nub (Element H-Nub and a Guarder rubber). I'd keep FPS levels at around 350, that way you can use the rifle in most CQB skirmish sites, as well as being able to use it in a more woodland setting without much of a disadvantage.
Well, this is my baby. ICS M-4A1 with M-120 spring and some minor internal improvements. As my CA was named "CArmen", I call the new carbine "Inez"
I made BBulletProof Polycarbonate shield for the scope, utilizing scope cover, PC AR-layers lens and my optician`s skills The yellow stripe on the back of sight base makes iron sights aiming faster, esp. with a bit fogged binoculars. The post is painted white, to make it visible on usually dark targets. The TM folding aperture is beneath the scope mount. The scope itself is 1.5-4.5x32 AO "RM" sight, that I bought for some 20 bucks and it really does the job The bipod is SRC Harris-type, I find it very useful.
I know that the camo is rude and ugly, but it works
The photo is a bit blurry, but it shows how effecive is camo The next photos I will always take with tripod.