I think you need to ask your self this question first . How many rounds do you think you will put down range in the life of the gun . This year alone I've shot 1,500+ rounds of 223/5.56 through 3 ARs . At the rate of 500 rounds a year any barrel will last many years . If you plan on only having 1 AR and shoot as much as I do . I would get a chrome lined barrel . When ever I buy a gun , I plan on keeping it for the life of me then handing it down to my son . I know it's stupid but I don't want him saying , hey I got all my dads guns but there all garbage cus he shot them into the ground . A chrome lined barrel should be good for 25,000+ rounds .A untreated chrome alloy vanadium barrel will shoot 10,000+ rounds . The melonite coated barrels expected life I do not know.
I would consider how many rounds you plan to put through the gun in it's/your life as well as what you plan to use it for .
If you plan on the gun being your HD/plinking gun and you plan to shoot the heck out of it . I recommend a lined/coated bore . If you plan to shoot competition and for accuracy you would not want it chrome lined and most likely stainless chambered in 223 wylde .
Hope this helps , if not never mind