There are no fucking tiers. There are dozens of different manufacturers which different degrees of compliance, deficiencies, or subjectively exceeding what is published of the MIL-SPEC and TDP for the M16 and M4 Family of Weapons.
They primarily cater to different sectors of the market, and though there is a lot of overlap - there are clear "class leaders" in their respective markets. Everything from game/space guns, precision high end boutique guns, fleet/production guns, hobby builder, hobby buyer, "I want to say I have an AR15 but will never shoot it" buyers, ect. ect.
Decide - while being honest with yourself - what class of buyer/shooter/consumer you are, and determine not only what the specific specs are, but why they are what they are, and determine whether that is something you do or do not need, because you will pay for it if you do.
Then look at companies and their reputations for QA/QC and CS, and you'll find it's really not as difficult of a decision as people make it out to be.
Considering nothing is in stock right now for a reasonable price - consider yourself lucky that you have the opportunity while you wait for in-stock items to come along to thoroughly get to know and research the information that is out there and widely available before figuring out what you want to put down your hard earned money for.
There's a lot of information out there, and most of it's easy to find with a modicum of effort, and when you can't find it, there's many posters more than willing to help you - but for the love of god, at least try Google before asking the question.
When you open a thread and are about to ask a question, please, for five minutes, stop - go to Google (most browsers have a convenient search bar already there for you) and type in the exact words you were going to use for your title before opening a new topic. The results may surprise you.
~Augee