No one caliber is "best" for all around usage, some will provide "overkill" and others, even at reasonable ranges may prove to be marginal at best. I think you might want to revisit this post with the "ammunition availability" and/or reloading components availability factored in, in light of the current wave of political hysteria in D.C. following the Newtown CT tragedy-
I have been evaluating another varmint rifle, and am closing in on the old .220 Swift and the later .22-250. I have ruled out the .223 because it is also a military issue round and recent surges in ammo sales have made the 7.62x39mm and also the 7.62x51mm NATO (.308 Win) possible candidates for the scarce option.
The time tested 30-06 is my first choice, the .308 Win. is also excellent, but as it is a military round (M-14) and the military no longer uses the 1903, the M-1 Garand or the BAR as in the past, I feel safer with the 30-06. I have 4 dependable and accurate rifles in that caliber, two are scoped-- a pre-1964 std. grade Model 70 and also a pre-1964 Featherweight Model 70- two are not- a 1903 NM Springfield and a post Korean War Garand (International Harvester) . I have over 2000 "loose" rounds and about 800 in the Garand enbloc clips--
I am surprised that neither the .270 Winchester or the 7mm Rem magnum were not mentioned- neither are Military issue, and availability might be better than the .308 in light of current scenarios. The SKS and AK-47 based 7.62x39 rounds are more suited to 400 yards or less, and shooting a large game animal with such a load is not a clean kill situation in most cases.
I would rule out the Weatherby Magnums, way over priced and the recoil factor is an issue. Also the .300 Win Mag, the .338 Win Mag, the .358Win Mag, and the old .348 Win (proprietary to the fine M71 lever rifle)--
If I could choose 4 Bolt centerfire rifles from my battery to encompass varmint, game and also the aforementioned SHFT Akron-Im (Savage (rifles) Have Fine Triggers) which I have found to be true, by the way--they would be thus-- Varmint- My Pre-64 M70 .243 scoped, My Pre-64 std. grade M70 30-06 scoped, and both the Garand and the 1903 NM Springfield. If Elk, Moose, Black and Grizzly Bear are going to be included the hunting picture, then I would drop the Springfield 30-06 and take my Mauser square bridge .416 Rigby with express sights unscoped.
Just one man's opinion.