I would go with the 223 if you plan to shoot a lot. Ammo it cheap and the 223 has plenty of range for most varmit shooting. For long range big varmits the 243 would have an edge but to me the 243 falls in the spot where its more than I need for varmits and less than I like for deer. Mine sits around an awful lot while I shoot the 223 for varmits and the 25-05 and 6.5 for deer. Although low in recoil, the 243 can wear on you in a long afternoon of Prairie dogging. If you don't reload, varmiting could get expensive with the 243 if you shoot 300 rounds a day or so like I do with the 223.