I'd say, arguably, AR's ARE the most versatile rifle ever produced--not necessarily the best
I'd argue that the most versatile, in terms of calibers possible, would be something like a T/C Encore. You could, if you desired, (and had the cash and the room) have every caliber from .22LR up through African elephant calibers.
Now, the AR being arguably the most versatile repeater? I could see that.
I met the civilian AR-15 in 73, and the M16A1 in 75. Small Arms Repairman trained, and I worked on a LOT of them, and inspected and checked even more. After my tour with the M16A1, I swore I would never own an AR-15. That lasted about half a dozen years, until I broke down and got one, because the accessories were so CHEAP. (ah, those were the days...
) A 30 rnd stick for a Mini-14 was $14.95. A 30 rnd stick for an AR/M16 was $3!
The original ARs were NOT the tack drivers common today. They were ok, but nothing special. Huge improvements have been made since then. I'm not going to go out and get another one, despite the fact it is likely a better rifle than the old style one I had. Its simply too much money for what its benefit TO ME, would be.
If you are curious, get one. If you don't like it, pretty much guaranteed someone else will buy it.