RE: 308 or 243?
The .243 with good hunting loads will take any whitetail PERIOD!
I shoot a .308 and a 7MM RM, and have seen great results with the 7MM-08. My first deer gun was a 6MM Rem. (Still sorry I got rid of it!)
This year after using the .308 and 7MM RM for years, I went to the .243, and love it! Kills 'em just as dead as the '08 and 7 MM with a lot less recoil!