308 for me cause when I bought my AR-10 the only two choices were 308 or 243 and I have no experience with 243. But I can tell you that I replaced a semi auto 06 when I bought the 308 and can tell no difference in normal range shooting. The recoil, especially with an AR-10 is way less. 308 fine for any North American Game and can be found fairly easily about anywhere. Military surplus rounds are common and cheap for practice shooting too, but many NATO rounds are for practice only and are not allowed for hunting. Hunting rounds are easily found in any big store.