Smith & Wesson M&P AR are an excellent firearm. I have one issued in my squad car. Stay away from the carbon model. They can be damaged much more easily. They are reliable but you will be better off with any other model. I have seen some of these rifles with over 5k rounds through them and they are still going strong.
As far as a hunting weapon, the 223/5.56 platform will kill a deer but shot placement is key. Even then many times the animal will run long distances before dying and with the small bullet wound will not bleed out much. Many deer are not recovered when shot with this caliber. I use my mostly for predator hunting. Really 3 rifles everyone should have is a 22lr (Ruger 10-22), 223 (bolt or AR platform), and a high caliber gun in 308 or 30-06. If I was picking just one I would go with a 22lr as I can get more ammo, and carry more ammo for it. It also offers more hunting opportunities. I can shoot a lot of squirrels or other small game that is easier to get with a 22lr, not much left with a 223! You can carry 5,000 rounds of 22lr in less space and weight than 1,000 rounds of 223/5.56