Bob S
Depends on what purpose you expect the gun to fulfull. For defensive purposes, a 12 gauge stoked with 00Buck & slugs is hard to beat. If you need to hit 4-legged varmints, I'd suggest a scoped rifle in .223, .22-250, .243 etc. For short range rifle work, a Mini-14, M1 Carbine or SKS might do the trick.
My $.02