My son is currently building up his "gun" account and looking to buy an AR/M4 type rifle after he gets XD 40. Ive not done any research into the brands, just suggested the M4 flattop over the AR style, this will be more of a plinker, SD, SHTF gun. Any suggestions on what brand to go with and more importantly what brands to avoid and why? This will be several months down the road so definitely not looking to buy at the moment.