Easy!
A properly set up Colt Government model in .45 ACP! I'd cheat and add a .22 conversion unit and since it would have to do the hunting too, a .460 Rowland Conversion unit and a dillion square B press.
That one would do the most jobs in one gun for me, from IDPA, to plinking, to close range hunting, self defense, CCW, etc.
Since it has often been my only gun over the last 3 decades, and I have a great deal of familiarity and trust in it, the choice is/was easy!
Jercamp45