RE: If you could have only one rifle, what would it be
I only owned one rifle and it is a 7mm rem mag (Win model 70 classic S.S). The .30-06 is a good choice but, if you plan to hunt antelope and take other longer shots at smaller game over 250 yards plus, it is not quite as flat shooting as others have mention. That not with standing the .30-06 might be a better choice.
.223 ??? That caliber is not legal in Colorado for any big game.