Deep subject with a lot of info to consider.
DD and Colt are top of the line and you can't go wrong...pony up the $$ and buy once cry once so to speak.
That said an AR is an interesting beast ....
The BCG and barrel are where the important quality items need to be....followed next by a good trigger/hammer unit.
Most other main parts like lower/upper/buffer tube etc, provided they aren't completely substandard junk, are all the same and no need to spend big $$ on. This is more an issue if you are building a rifle from scratch...which can be a fun, cost effective way to arrive at a finished quality AR at the most affordable price.
You also need to decide what style/size/type of AR you want to end up with so you don't buy the wrong rifle and then spend further $$ swapping out parts and or upgrading to get what you want.
Shorty cqb rifle, M4 variant or other 14.5in basic rifle, 3 gun or other gamy ~16in variant, Longer/heavier barreled precision/DMR sniper type of rifle??? An AR can be any of these...and sometimes multiply if you are prepared to buy multiple uppers.
Without a budget parameter and or basic style of AR stipulated its hard to recommend.
Some won't blink an eye at a $3~$4 AR as well as dropping another $1500 customizing it. Others may want to stay under a grand.
Don't forget optics and or sights.
Fixed irons, buis, red dots, compact low power scope or high magnification precision scope???? Any AR other than a dedicated precision optic rifle requires at least buis.
The beauty of an AR is that it is modular so any part of the rifle can be upgraded, swapped out, changed, repaired etc easily and without gunsmithing. The occasional special tool makes life easier on the rifle and man but the AR can be worked on/built/repaired with basic hand tools and in a lot of cases bare hands by the average joe with a lil knowledge and homework.
Sadly they are exclusively a range toy for Canadians so beign the absolute toughest/heavy duty isn't nec worth the $$. If a small part and or component fails it can be remedied at the range if you have spares and it wont be risking your life or other serious consequence when it does....unlike a military or self defence application out in the field. That's where the highest quality/milspec expensive AR rifles earn their considerable price tags.
Super fun rifles to play with/mod/customize etc....truly an epic shame they got restricted....they would be SO much more fun to play with unrestricted......hunting/survival/plinking etc.....and all ARs are takedowns by design which is also cool.
Be prepared...its a major rabbit hole yer about to go down....
