I have been a .243 lover for years, since about 1958 or so when a friend handed me his model 70 and a bag of 243 ammo. Talk about a way to impress a young feller.
I have a very good shooting .243 RUGER "flat bolt" sitting in the rack right now, so in no way can anyone say I am against that caliber.
Been there and done that and have a number of deer, Mule and whitetail, taken with the .243.
Favorite "hunting" bullet being the 100gr Nosler Partition.
Great rifle, easy on the shoulder etc. etc. love it!
However, without knowing more info from the origional poster, and just going by what they said, I'd still come down solidly with the "06".
It is a rifle with a much broader ability then sub .30 caliber rifles.
Lots of great calibers out there, but if I could have only one it would need to be the one that opens the greatest number of doors.
30/06, 100 or 110gr. varmit bullets all the way up to the 220grain big boys.
.243, very fast varmit bullets of 55gr, up through varmit bullets in the 70 - 80 grain range and respectable hunting bullets in the 90 - 105gr range.
While some have taken elk sized critters with the .243 and some practiced marksman, who carefully PICK their shots, have done it many times, few would call it an "elk rifle", even as good as it is.
Yes, I like the .243, but if anything bigger then deer was in the future and I must remain a one rifle hunter, sorry, it should be something bigger.
Keep em coming!
Crusty Deary Ol'Coot