Two Barrels, one rifle, one pistol?
Pistol, no doubt, 460 S&W due to the versatility as mentioned
Rifle-
375 H&H, I will evenetually get one of these. It can do anything, and load it light.
If you felt that was a bit much, 30-06 tops 308 for me, heavy weight bullet selection.
But 2 barrels? I think the addicition will grow greater than two barrels. It's like ruffles, bet you can eat just one (or two, or three).
JW