If I were to have only one, it would be a .308. Without a doubt, it'll do more than either the .243 or the .30-30. If ya really want to know my preference, it would be the .45-70. It'll do more at greater distance than the others. You've got to sit down and learn it, and best to reload for it. If you're shooting coyotes for the pelt, forget it. You'd have to sell it in two halves.
I'm not a great fan of 6mms (.243s). To me they are a nowhere caliber. Too big for varmints and too small for big game. I traded a 6mm for a .308 years ago and never looked back. The .308 has taken more deer than any other rifle I own, plus coyote, fox and woodchucks at 300 yards +.
I've killed quite a few deer with my 6mm., but the .308 kills them deader, quicker, and the .45-70 more quicker and more deader.
Pete