Revolver- 357 mag, It is extremely effective and you can load 38s in the same gun
Semi auto pistol- Even though I hate to do it, I gotta say 9MM, it's ballistically acceptable, there's a lot of it, and prices are reasonable
Rifle- 30-06, it has a wider variety of applications than the 308- 7.62 NATO, the only downfall is it requires a long action as compared to 308's short action.
Shotgun- 12g for sure. Huge varieties of ammo for all applications and powerful enough to get the job done