I'm assuming you mean an M4 GBBR? Cause there are a few other models out there as well (i.e. AK, MP7, SCAR, etc...)...and probably a lot more coming out soon.
I like the WE M4. So far the ones I've seen have worked out of the box (but they were all Gen2+). Metal quality is decent...receiver finish wasn't jaw dropping, but I'm not a wall-hanger kind of guy.
The WA/Ino/G&P's look great. Reliability out of the box might be iffy...not an issue if it's a wall hanger. I'd bet they run ok on duster for the occasional blasting. TONS of upgrade/replacement part available....because upgrades/replacement parts are needed.
AGM's are just fine for wall hanging. I suspect that they'd need a bit of upgrading/tuning if you were to use it regularly.
If you want a wall hanger pistol...WA's are really tough to beat. They're really sweet. A TM 1911 base with a full metal kit will run you into the $600 range...if you can find good deals on stuff. With GBBs, you often get an imperfect blend of looks, durability, performance, upgrade potential....there's no pistol out there with it all right out of the box (although so far as 1911's go the TM 1911/MEU is pretty sweet...just that metal kits are $$$).