Depends on what you want.
The 300 win mag in Rem 700 is a good choice.
So is the 308 in AR 10.
Both have been getting the job done for a very long time...and ammo and components are easy to find for both....not so with many of the new calibers.
I have both, and others as well.
Most do not stop with just one to get it all done.
But if I had to choose it would be a 308 Win.
Why? Ease of getting ammo and components. One can find ammo, out where people target practice. In an emergency, ammo can be acquired most anywhere.
Components are everywhere, cheap, for reloading, and it uses a small amount of powder compared to a magnum, and works with a large variety of powders...military surplus bullets, powders, and LC cases by the thousands.
Many serious job has been accomplished by the 308, it's a good working tool.
On video, the Australian LR shooting couple took the 308 to 3000 yds with 2 hits out of 10 shots...about as good as the rest of the calibers.
Others calibers are better at specialized events, so I have a few of them.
But a 308 will get it done, and allow one to practice, cheaply.
I can build any rifle I want in any caliber,
so my # 1 rifle choice was a bolt action 308 9 twist barrel 22" long Rem Varmit contour with a trued 700 Rem action.
200 gr SMK .715 BC at 2740 fps... 2.990" COAL is possible with MDT mags.
Then hybrid cases can be introduced, for more performance.
One can bulid a 308 on a long action or short action. Over 3600 ft/ lbs of energy available from this case, if desired.
I have 8 308s, no other caliber is close, I built them all, for specific purposes from. 16" to 30" barrels, 12 to 8 twists...in both AR and bolt, long action and short action, the bolts are all trued Rem 700s .