To me there isn't any doubt it's the 30/06.
Ever since it was conceived its basic case has been necked up, necked down,Improved, shortened,and been the parent case for untold wildcat and factory permutations,each one offering some real or imagined benefit over the original.
Its ballistics offer a baseline from which we can establish ballistic thresholds and the 338 or 375 are really nothing more than 30/06's with heavier bullets of larger diameter having similar velocities and trajectories.
Going the opposite direction we have things like the 270,280, 25/06,all of which go a bit faster,shoot a bit flatter,and kick a bit less.A 7x57 or 7/08 both have ballistics about like a 30/06 but with slightly lighter bullets(yes I know the 7x57 was the inspiration for the 30/06 and came first but has not had the same number of off spring). Popular cartridges like the 7mm and 300 magnums were designed to better the 30/06 but that cartridge still set the baseline to beat.
All of these are refinements on the original but I bet if we took them all away and forced hunters worldwide to use nothing but a 30/06 for a season the annual "take" of big game animals would not change much.
And a guy who can shoot,with his pockets full of 180 gr expanding bullets and the other pocket loaded with 220 gr expanding and solid bullets,can safely hunt any game animal on earth from elephant on down,giving it an undeniable advantage over anything in a smaller caliber.
Yet the cartridge is generally over looked for specialized purposes (we choose something else) and because we have so many choices, it's easy to look past the 30/06(i.e. "underrated"). But none of this changes the fact that the 30/06 is capable of accomplishing many(most) of the chores involved in BG hunting.
