I've built better ARs for the same prices as both. Both are quite pedestrian.
There are so many "cookie-cutter" ARs out there that they're almost indistinguishable.
My .02
Yep, the incestuousness of barrels and receivers etc make it where there really are only about 5 or 6 companies making barrels and receivers for most of the name brands.
Some have gone in house after farming out in the past, ironically enough, PSA of all people is using FN barrels last I heard, abandoning Aero Precision.
While S&W initially white labeled Stag Arms rifles in 2006-2008 before moving production in-house.
If you bought a M&P 15, Ruger 556, IWI Zion, Sig Sauer Tread, Windham Armory, and didn't pay much more than 700 bucks, you probably have a decent basic rifle that will get the job done for most and didn't break the bank.
No one should over think their first first AR that's for sure.