Like everyone said they're both built to the same specs, the only thing different is the name on it. Have you ever thought about building your own? My son just built one. He bought a S&W M&P lower locally from a gun shop, it's the only part that's serialized. Then he picked up a 9MM upper from a guy on AR15.com. He went to a gun show and bought the trigger group, stock, flip up sights, red dot sight, and magazines. By doing it this way you can buy the accessories that you like. He doesn't know it yet but I picked up a free floated forearm for Christmas for him. It's a Yankee Hill Machine Black Diamond that's midlength in size.

Since everything is built to government specs there really isn't much difference in quality between brands. By building it yourself you will have the satisfaction of doing it, as well as the fact that you can buy exactly the accessories that you like, not what the manufacturer puts on it. You'll also spend less money doing it this way. Check out AR15.com for in depth info about these guns, they are a great source of info.