I enjoy building and shooting my AR rifles and pistols. The pistols are in 5.56 and 300 blackout and the rifles are 5.56, 6.5 grendel and 7.62x39 Russian. I also have an AR57 upper in 5.7x28 that uses FN PS90 fifty round magazines.
I like Palmetto State Armory lowers, their uppers are good too, along with Radical Firearms for the 7.62x39 and Model1 in Texas for the 6.5 grendel. You can pay a lot more for a very small improvement in quality, but most ARs shoot better than their owners, especially if you take the time to set them up and feed them good ammunition.