re: AR Upper/Lower Kit Brands

It depends on what you want to do with it. If you want something accurate you'll want to pay attention to the barrel and probably get a decent trigger, which means an aftermarket trigger, not a lower parts kit with "polished trigger parts". Lower parts kits typically include the basic trigger group but you can find some without it for a small cost savings.

Anyway, if you want something to put a bunch of rounds through and you don't care about bolt action accuracy, get a chrome lined or nitrided barrel (or upper assembly) from any of those you mentioned. For a plinker I personally wouldn't pay Daniel Defense prices but that's your call. Above a certain price you're paying for the name, exact anodizing matches, etc, not more functionality.

If you want something accurate I'd look at Larue or one of the match barrels from Rainier Arms; there are plenty of other choices as well. For a trigger I prefer Geiselle but the Larue is almost as good and a lot cheaper. If you're assembling your own upper you'll need an armorer's wrench, a vise, a vise adapter for an upper receiver and a torque wrench. That's why upper assemblies are popular.