I've had a couple G&G's, an older m4 and a new m14 ebr. both very reliable, the m4 eventually did break but only after a lot of heavy use. the m14 has been my primary for 2 seasons (shared duty this year with PDR from magpul) and has performed flawlessly. I have read many reviews on their newer guns, even the lower cost ones draw great praise.
Personally I recommend G&G. some reviews point out that some of their models aren't as close replicas as some other brands but it's usually in the name of practicality and useability as an airsoft gun rather than perfect replication of real world guns(most ppl can't even tell the difference especially since everyone rushes out and aftermarkets the hell out of their guns anyway!)
My m4 took standard mags and all internals were readily available and compatible with most other m4 parts. The m14 is a little different, the mags are G&G and classic army only. but they aren't hard to find. the gearbox internals are standard for an m14 however it has a proprietary motor mount. mine has not been an issue but is said to be a weak point. I've checked availability of the part just in case and seems readily available too.
Last edited by targetGspot; October 20th, 2013 at 16:56..