If you want an AR / M4, yeah definitely the G&G Combat Machine. Not exactly the most unique, but can't go wrong with them!! Would be a great choice. Wish I'd got one myself rather than the shite CYMA (cost me more than a G&G would as well....)
Alternatively yeah CYMA AKs are basically the AK version of the G&G M4s I guess you could say? They're the other gun that gets recommended a lot, good value and quality.
If G36s are your thing, JG ones are tough and very reliable from what I've heard (reason why lots of sites have used them as hire guns)