The reason Real Sword are so durable is that their externals are all real steel grade stuff. They are the ONLY company that make airsoft guns of this grade, and unfortunately don't make an AR model. Although if they did, I would be on that like Michael Jackson on a troop of boy scouts.
Your best bet would be either Classic Army or G&P. I have a CA, and honestly, from all the different ARs that I've handled and shot so far (PTW included), I rate it top of the pile. The quality of the metal and plastic is beyond anything else out there IMO. And unlike a PTW, you don't have to handle your gun like a porcelaine doll for fear of cracking your receiver or keeping it dry for fear of shorting out your electronics.