Both great cartridges. I have two .30-06's and one .280. I used to hunt deer with the 30-06 years ago, but lately find myself using it most often for elk. I've used the .280 mostly for deer and antelope. But there is a lot of overlap between the cartridges so either one can serve well for almost any American big game.
The choice of which to use when is mostly about personal preference.
