Since you want a midlength I'd recommend a 16" barrel which is perfect for that gas length and will avoid the need to permanently attach the muzzle device.
Solid advice. I've never understood why anyone would want a 14.5" bbl with a permanently attached long flash hider when a 16" bbl with a regular flash hider gives about the same overall length.
I have two 16" ARs, one with carbine length gas system, one with midlength. They both function perfectly. IIWY, I'd go with a 16" with midlength gas system.
Violence is an ugly thing, but not the ugliest of things. The decayed and degraded state of moral and valorous feeling which believes that nothing is worth violence is much worse. Those who have nothing for which they are willing to fight; nothing they care about more than their own personal safety; are miserable creatures who have no chance of being free, unless made and kept so by the exertions of those better than themselves. Gary L. Griffiths, Chief Instructor, Advanced Force Tactics, Inc. (Paraphrasing John Stuart Mill)