You seem to be looking for a rifle that will "do it all," so to speak. If you want an 18" barrel, a really good choice, in my very humble opinion, would be one of the following:
1. Larue PredatAR 18" - Lightweight, lightweight profile barrel, accuracy will be very good. It is a lightweight profile barrel, so accuracy may drop off a little if the barrel gets hot. How much if at all, I can't say.
2. Larue PredatOBR 18" - Hybrid of the PredatAR and the OBR, which is a heavier rifle more suited for precision shooting. The PredatOBR will have a heavier profile barrel, so it should maintain more accuracy with a hot barrel.
3. A lower of your choice with a BCM SS410 18" upper - Find an lower that is set up the way you like (A2 stock or collapsible, two-stage trigger, etc.), and buy a BCM upper. They are mid weight profiled barrels, and I really have read many accounts of them shooting subMOA groups with the right optic, trigger, and ammo. They use the USMC SAM-R chamber, which IIRC, is very similar to a Wylde chamber. That means it will handle 5.56 and .223 rounds. If you go this route you should note that BCM sells the uppers without a BCG and charging handle. I would buy the upper with a BCG so you can have them headspace it.
Any of these set ups would allow you great accuracy, and I would be proud to show any of these set-ups off to peers
I personally am setting up a precision-oriented "do it all" with a Spikes lower, a SOPMOD stock, Geiselle trigger (probably a SD-E), BCM 16" SS410 barreled upper (haven't decided on handguard), and either 1-6X or 2.5-10X scope.
It is taking me a long time to gather the funds, but I know it will be worth it!!