[Zack The Ripper]

King Arms makes good M4's. Not fantastic, but good and fairly reliable.

However, VFC makes the best, hands down. Out of the box you would need little more than a spring change to get it within field limits, and if you want to take it one step further, a quick shim job and regreasing of the gear box while swapping that spring out. Other than that, it works perfectly internally for a factory stock gun. The externals are much better on VFC than pretty much every other brand of AEG. The only one that comes close is G&P, but VFC has more stuff closer to real steel spec than G&P does, and VFC is compatible with much more externally speaking.