I bought one of the very first-generation STAR G36C's when they just started to hit the market in Asia and I still have it today. It has suffered through several self-inflicted disasters, and it still works just as good today as it did then. I have come to think of it as one of my most reliable AEG's. I don't believe it's made with super craftsmanship, though - it's just survived what I believe any decent AEG (for the money) should be able to stand up to.
I can't give you any specific comparision to a G&G M4 because I've never owned one, but I can give a broad suggestion when it comes to any Armalite comparison.
The primary fault of any G36-type in airsoft is accessibility. Out of the box, you have fewer options when it comes to magazines, batteries, and aftermarket parts. Armalites are just more widely supported, that's all. It's not a big enough problem that you should eliminate a G36 from a possible purchase, but it's something to think about. Before buying any new gun, I recommend taking a look at all the additional purchases you may have to or would like to make, in order to get a weapon that fits the idea in your head.
Personally, I typically use a Guarder Enlarged Handguard so I can use a Large-type battery, and I have an Armalite MagWell Conversion also as an option. These aren't exactly authentic modifications but I appreciate having them, for flexibilty's sake.