I'm assuming the cost of blasting thousands of rounds/month is not the primary consideration - ie cheap. I'm considering versatility, availability, job effectiveness, and overall cost-effectiveness. I'm also not sure if you're asking for 3 choices per category. If not, just take the first one.
pistol - .40SW, .45ACP, 9mm
rifle - .308, .223, .22LR or one of the above in a PCC
SG - 12Gauge, 20 Gauge