I've owned 3 G36Cs in the past years. I'm just going to put it in straight plain words. It's up to you as to how you take it.
-Marui makes by far the best quality G36C, hands down. It has to do with SO much more than just gearbox parts.
-I've worked on dozens of Classic Army G36s, and owned one myself, and the only thing nice about them is the fiberglass/ABS externals. Everything else is a complete headache.
-Star G36Cs, no matter what people tell you, are just a waste of money. They're not very good guns, externally or internally. Buy a JG or Marui long before you consider buying a Star.
-KWA G36s are decent guns. They may or may not be worth the extra cost. It all depends on how you look at it. I'd still take a Marui.
-Echo1 = JG, plus battery, charger, and a warranty. That's all. In my opinion, they're better quality than CA or Star, which is silly, because they're so cheap.
The only other option I know of is the SRC, and I have no dealings with them. Chances are they're just like all their other guns, which means they're hit or miss: pretty good, or complete crap.
If you're an airsoft noob, just go buy an Echo1. You won't regret it. They're decent guns, I've seen very few consistent problems with them, and they're cheap. If you want something high quality, look at a Marui.
-BATMAN