Best all-around rifle
Seems to me that to qualify the rifle would have to be able to:
Be carried by a wide range of carriers some distance
Be effective in shooting animals (4-legged) for nourishment and (2-legged for turning the odds and winning a battle) as well as roughing up their vehicles of all types.
A simple loading technique with a reasonably high capacity so that you can stay in the game longer (that is, removable mags)
THe ability to load (loading done by someone else)in parallel with shooting to stay in the fight continuously
A round that can take down large animals and can penetrate barriers before hitting it's target (within reason)
A round that can be shot from a mid-priced gun that can be tuned for reasonable accuracy and be altered for a surpressor.
To me, this leaves the .308 front and center with it's ballistic friends 30-30 and 300 win mag as alternatives. My favorites, the 335 lapua mag and the 300 RUM just skew too much to high power uses to be broadly acceptable just as .223/5.56 skews low.
I'd pick an FNH FNAR as a gun that appears a 'tweener' caught between military and police rifles and modern hunting rifles. Safer looking in a crowd than an M4 - depending who carries it. Or it's shooting grandfather the Browning BAR which would be offputting to very few.