It is worth mentioning the M14 variants here, since the OP did not clearly say it has to be an AR, though he talked alot about AR. I am on a similar quest.
I have concluded that I will eventually need two different NR rifles:
A .223 AR, probably the Swiss, but maybe a different one.
A .308 rifle, which will probably wind up being an M1A/M14, but I might go for a bolt action .308 variant
The question now is really whether it will be exactly those, and the big question, which comes first

OH the pain of limited budgets.
The RA XCR is interesting if you got a kit you could flip between .223 and .308, and people who own it seem to like it. I am not as drawn to this option because, unlike the above two options, no army in the world has ever fielded a RA XCR so it is not as "proven" as many of the other options on this thread.
The M14 is not so much "tacticool" as it is just a very classic military look. Right now I am leaning towards starting with the SA mostly because the .223 ammo is cheaper.