I shoot the Colt AR-15 Competition Match H-bar with a 20 inch barrel and it shoots flawlessly. I have the EOTech 552.A65 Holographic sight and boy does it shoot sweet.
My son just purchased the new Bushmaster and says its the sweetest rifle he's ever had. They say Bushmasters are put together by Gorilla's. (Rock Solid and tight)
However, I don't think you can go wrong with a Rock River Arms either. These would be my first three choices and in this category too.
The AR-15 223 Kicks butt:
I shoot Large Michigan Deer with my AR-15 every year and I'm not kidding when I say the deer drop faster with the 223 round than any other caliber. This has been my experience on my 125 Acres in Cadillac Michigan and 20 acres in Milan, Michigan. We shoot lots of deer here all with the mighty 223 round.
The BlackHills 60gr Soft Points work very well and the new DRT Ammo just makes them collapse the second the bullet hits em.
For home and range I like a SIG-522 in .22 LR. Gun is inexpensive, ammo is inexpensive, if used for home defense the .22LR and 25 round mag. is just right.
I like it for fun on the indoor and outdoor range. And for small game hunting. Once someone sees it they want one.
The two calibers you mention (223 & 308) come on different platforms. The 223/5.56 Nato (along with the 300 Blackout a few other caliber choices) are part of the AR-15 platform. The 308 (along with the 260, 243, and several WSSM calibers) are part of the AR-10 platform. As a general rule, whether you are buying or building, the AR-10 will run you about $400 more than a similarly equipped AR-15.
I own a couple of these units and they are fun to shoot. However, I do not use them for home defense. The 223 will blow right through an 8" tree trunk. Can you imagine how much drywall and studs a round would blow through before stopping? It is a round that is difficult to control inside the house and would leave it looking like Swiss cheese. Even the lowly .22 cal will penetrate completely through four 2x4 studs stacked back-to-back at close range. My personal choice for home defense is a short-barreled (18.5") Rem 870 with BBB lead shot.
As for the purchase of the AR-15, they are pretty expensive right now (nearly double). If it were me, I would wait for the panic buying to stop and for prices to come back down. I don't see wide support for a full-out ban on "black rifles" in Congress. What may be more likely is a ban on high capacity magazines. Of course, my thoughts are skewed because I already have a couple AR's. It's a roll of the dice for you, but I would wait and see.
Rock River Arms is hard to beat. Although I have a Spikes Tactical in an M4 version that has performed flawlessly. And a SBR I put together using a DTI lower, DPMS upper with an 18" stainless steel 1-8 twist barrel. Both are chambered in 5.56. The SBR will put 5 shots in 5/8" groups at 100 yards.
Check out CPWSA dot com! They have designed an AR that is already tricked out for competitive shooting so it has a sweet trigger and there are reports of crazy accuracy from their custom barrel (one of their sponsored shooters is a 14 year old young lady who can shoot circles around most folks...reports are she is getting half inch groups at 300yds). Mine is 1/2 MOA all day as long as there is little wind...I am not a wind whisperer!
They only built a few and not many are left from what I hear. As I recall they are built on JP matched upper and lower. I have one and it is far better than my RRA and Bushmasters and needs no upgrades other than your choice of optic. CPWSA also has that figured out and recommend the Burris MTac for 3-gun style activities with the 1-4 power and dead on stadia tree in the reticle.
I got a Bushmaster and a Colt and both are 5.56. I have had the Bushmaster for about 3 years now and never had a single issue yet. I have only had the Colt about 3 months, so I haven't had alot of trigger time on that rifle yet but so far I have put 200rds through it without a problem. Good luck on your decision but be careful AR's can be very addictive lol!!