ARES and CA are the best G36's out there.
Externally they're very similar (glass fiber, nice texture) and that's where the huge advantage is over TM/JG/etc. Even if the internals aren't good (which they are in both, I'm pretty sure) you can always replace them.
Replacing externals, like a receiver, is much more difficult.
Airsoft Sales and Repair/Upgrade Services