This comes from a guy that is yet to shoot anything with his rifle, (except a lot of EZ-C targets) BUT, all the research I did before buying my rifle brings me back to the .30-06. Unless your budget allows you to purchase multiple rifles, the .30-06 offers the widest range of calibers than any other rifle. You can get 90 grain rounds to pop coyotes with, all the way up to 220 grain rounds that can drop an elk in its tracks. There are just not a lot of rifles that can do that.
It's true that the '06 is one of the most versatile cartridges out there, but if a hunter were sure that he'd be hunting only deer-size or smaller animals, he'd probably be going with more gun than he would ever need. The 6 and 7 mms (not magnum) and .270 (not magnum) calibers are generally easier to shoot and are more accurate in the hands of a novice. In my opinion, one of the biggest mistakes a hunter can make is getting a big rifle before learning the "basics" of good shooting skills. In fact, starting with too big a rifle is the quickest way to learning BAD shooting skills! When I was a full-time taxidermist, I met dozens of hunters who just couldn't kill game cleanly because they were shooting big rifles that were controlling them, instead of the other way around.