Olympic makes:
Olympic
SGW
Tromix
Palmetto (PSA)
Dalphon
Frankford
Century (Old)
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Things change over time.
This chart looks very out of date considering Olympic went out of business in early 2017.
https://en.wikipedia.org/wiki/Olympic_Arms
OEMs change constantly so it is really hard to keep up with who is really supplying who so much so I stopped trying to figure it out long ago.
The important parts for an accurate/ reliable AR:
Barrel, BCG, Gas Block, Trigger Group
What are you getting with preimium lower / Upper receivers are the fit and finish. If it's a complete lower, then the parts used are going to be a better quality if buying from Larue or another high end builder.
You could build a cheap accurate AR with a PSA upper / lower as long as you're using a quality barrel and BCG.
Hand guards, as long as it free floated and doesn't flex when you preload the bipod, you can get away with cheaper, but it's probably heavier material.
Another thing to consider with ARs, is that if you're shooting milsurp type ammo, you're not going to get sub MOA groups, it's 3 MOA ammo.
This is a much more informative post. There are a lot of real pearls of wisdom in this one. I will add a few things. People get really hung up on what is "the best". When you move up the food chain in AR15 lower and most other parts what you are getting for your extra $$$ is fit and finish of the final product. For example I have never picked up an Anderson Lower and not found what BCM, Noveske or even S&W would consider a blemish. They are not defective but show tooling marks and nicks etc.... They are on the low end of fit and finish of AR15 lowers but you can get them on sale for $30. That said for the most part they work as well as any other lower they are just not a pretty.
One of the big parts that the OP is missing is that building an accurate rifle is more than just assembling parts from a kit. When you buy complete uppers or complete rifles from top tier manufacturers that is what you are paying for as much as you are paying for the parts. You are paying for a name brand and the quality control and expertise that went into building that rifle. This is not to say you can't make a accurate rifle out of lower end parts. When someone does their own build from premium parts you don't really know if they had the expertise to put the rifle together.
IMHO your budget and realistic intended use of the rifle should drive your decisions in terms of the base platform, gear and accessories. Be realistic on what you are going to do with your rifle. If you are going to shoot less than 500 rounds a year what advantage are you gaining from a billet lower? You are never going to shoot a forged alum lower to failure. Honestly your needs do not demand the highest level of gear. If you are an "operator" in foreign lands filled with sand then your needs might be different and certainly more demanding. For me I am looking for reliability and quality in my rifles. As with almost everything there are laws of diminishing returns in the AR15s. Once you get past a certain point you are paying a lot more $$$ for very minor differences.
I am a minute of man shooter in the AR15 world. I am not a go out to the 300 yard range shoot off a rest and make tiny little groups kind of guy. I am a standing from the shoulder hitting man sized targets at 10, 15, 25, 50, 100 and 150 yards with varying levels of speed. What I really want is reliability when it counts. I want a gun that will be able to do this in a harsh environment if called upon not just on a square range on a nice sunny day. I buy gear that meets that need. So know your need and buy gear accordingly.
As MadMardigan pointed out ammo will make a huge difference. Most plinking ammo which is what most people shoot will give you on avg 3" MOA at 100 yards in most rifles. Some rounds will get better results with some ammo. You have to shoot enough stuff to know what your rifle likes. Just because Wolf Gold shoots 1" groups in my Colt does not mean it will shoot 1" groups in your PSA or BCM.
The Bolt and the barrel matter IMHO a lot more than the lower. For 99% of people if the lower is made to the right spec it will work as well as any other. Some will have a prettier finish and a cooler logo but functionally IMHO will be the same. YMMV
