That's a mighty wide open question.... "... a main rifle for defense, hunting, plinking, or formal target shooting"...
I can't imagine there are many of us that use an '06 for defensive purposes. It's not exactly a plinker either, although it's certainly a hunting rifle.
I have numerous hunting rifles, some of which are perfect for certain game. If the SHTF and I HAD to grab one rifle and one rifle only in order to put food on the table, ALWAYS function, have available ammunition of many types, etc., it would likely be my '06. This of course does not get into the argument about shotguns and .22RF weapons of any sort. I know I could do most anything with the '06, but it's not exactly a pleasant rifle to shoot for recreation.
That's my thought anyway.