I cant help you with .243 or .30-06, but in addition to the .45/.38 m&p mentioned above, I will say I find .380acp is about as easy as it get to reload for, surprisingly. Just be sure to check the cases thoroughly if they are range pickups (and afterwards, once you start reloading the same case over and over) as some .380s tend to beat up cases pretty hard.
You will have great luck with HP38/W231 (same powder) and N320 in both your .45 and .380 (and the aforementioned .38, if you have that caliber).
Both are equally accurate. N320 is much more expensive, but cleaner. Both are outstanding.