and like a tractor, which one is for you?
Start with what caliber would you like?
you have flat top and handle...and which sights for each? LOTS of options in iron, scope and red dot.
Adjustable stock or not, free float barrel? And then which stock, what barrel cover..mlok or ???
and what color do you want your furniture?
what length barrel? What profile? What material?
Trigger..stock ones are very gritty. The palmetto armory one is nice and on sale for $40 often. You can spend $250 or more on a trigger also.
My cheapie I put desert furniture on, red dot, palmetto trigger (and it's trigger went to my SW mp-15/22) it's light and handy.
My target rifle has SS barrel, A2 stock, 4X scope for competition, ambi bolt release, I have the 1/4 MOA handle/iron sights for it as well. and weighted stock.
SO many variations, option and such like it can be hard to know where to start.
Like a tractor, WHAT ARE YOU PLANNING TO DO WITH IT? is where you start.
The SW MP rifles are great all purpose/general purpose place to start. I have the MP 15-22 and love it, but it has limitations (too plasticy).
An AR-15 doesn't really differ from any other rifle. Its like the difference between tractors, some do things one way others another. But is also like a tractor in that you can bolt a FEL to the tractor, then you can bolt different buckets, hay spears, forklift tines, grapples, etc to that. And then there is the 3-point hitch on the rear that things not yet imagined can attach and be powered by PTO. The AR platform is that kind of flexible. And like a tractor an AR is not too pretty to get dirty.