"Best" can't be claimed without being assigned a mission.

For me, the "best" rifle cartridges I have owned have been;
22 LR
223
270
375H&H
(9.3X62 would be in there if I'd ever owned one, but I am going to fix that deficit soon)
404 Jeffery. or 416 Taylor

Best handgun cartridges for me have been
22 LR
357 mag
44 magnum.

Best shotgun for me is 20 gauge.

Best all around muzzleloading caliber for hunting of small game 40 cal.
Best all around muzzleloading caliber for hunting of big game 62 cal