I'd say go for the G&G, I've got a G&G MP5 and M14 and they're both perfect, not even bothered upgrading them, still running them entirely stock, not even changed the barrels or anything.
I've had nothing but bother from my G&P M16A3, doesn't feel that great in my opinion, too light and they're not 100% accurate to the real thing, I've had to buy a tight bore barrel and new hop and the range is still terrible, it performs weakly compared to my other guns and I've had to replace the piston, piston head and spring straight from getting it.
Though I did buy second hand.
G&P have nice trades and pretty demonic rates of fire, but my vote would be with G&G every single time without fail.