I've had experience on CA, G&P, G&G, KWA and Dboys M4s.
The best metal body I say has to go to CA, they have a really good design that holds the hop up unit in place properly(Improves accuracy). Fitment was quite good too.
G&P used chalk paint and It felt weird, and there were gaps between the upper and lower receiver. This is a problem because if you drop the gun in water, the liquid will soak in much faster and with much more volume(And since it's at the back of the receiver, it will go straight to the mechbox). Also, it will wiggle, which causes accuracy problems.
G&G's magnesium receiver, kinda sucked. Felt like plastic and it was thinner than other brands. Everything was okay, just okay, nothing to brag about.
KWA needs major reconstructive surgery if you wanted to use a one piece hop up unit, which is okay if you dont want to. Fitment is pretty good with anything really, and external appearance and quality is identical to CA.
Dboys is probably the second to CA. If I were to build a scratch M4 today, I would probably use Dboys over any other metal bodies(I would choose CA if they had more markings and costed less...). The new version doesn't have a gap between the upper and lower receiver. Fitment with their own Aftermarket gearbox is superb. No filing down the mag well was needed either, everything fit. External feel is identical to CA and KWA. Quite superb imo.
If I were to rank from best to worst...
Last edited by Skladfin; October 13th, 2008 at 23:43..