^ This, +eleventybillion.
Mission drives the train,
@justahop .
There's a difference if you're putting together a gun for defensive/duty, or serious competitive use - versus just hobby "fun day at the range" kind of stuff. Similarly, a serious training beater will lead a very different life from a safe queen. Each of these "missions" will skew your gear selection, even with budget in-mind.
Parts are not just parts, and this is the absolute truth with everything from the barrel and bolt-carrier group (BCG) all the way to the smallest springs, detents, and pins, and even to the "chassis," the upper and lower receivers.
If anyone ever tells you that parts are just parts, refer to this video:
^ I explain what this video has to do with your question, in my reply to
adam sr in this post -
https://www.thearmorylife.com/forum/threads/lets-see-your-ar-setups.258/page-5#post-4715 in that "AR setups" thread.
It's not about where you shop from, necessarily, but
what you get.
So before we go down the path, let's decide why you want the gun: what do you want it to do, for you.
And then let's set a budget, so we don't get too carried away and stay within the realm of the real.