The Colt 6920 is as close as you'll get to a real M4 without NFA paperwork. It's darn near a USGI M4 carbine with a semi-auto fire control group (instead of burst capable), and a 16" bbl (instead of a 14.5" bbl). For a hard use defensive carbine it's a heck of a buy.
But it sounds like you want a recreational use AR, so the M&P-15 Sport is a great option for what you want. You don't get a dust cover of forward assist, but the utility of those features is debatable. I actually prefer S&W's black nitride bbl treatment over hard chrome lining because it's just as durable, but it doesn't reduce accuracy like chrome lining can because of variances in thickness. S&W uses 4140 steel rather the mil spec 4150 steel, but unless you're shooting shooting high volumes of ammo, rapid fire, on a regular basis it's not going to matter. The Sport doesn't have heat shielded hand guards, and you will feel bbl heat even with light shooting with those. So, I'd spend the $20 to get a set of CAR or M4 hand guards with the aluminum heat shield(s), or get a MagPul MOE handguard which has thicker plastic and a larger interior diameter.
The M&P-15 T with standard forward assist & dust cover, the 1:8 twist black nitride bbl, lightweight free float hand guard, and included MagPul MBUS sights may be the best all around out of the box rifle for another $300 over the Sport. Whether you want a free floated bbl with faster twist is something you'll have to decide.