Ashe nailed it here. The better price, availability, bullet/weight weight selection, and versatility of the .30-06 puts it ahead of the other cartridges, IMHO. Most people rarely, if ever, make a shot out past 300 yards. The .30-06 is plenty flat enough within that range. You can go from varmints all the way up to brown bears (you can, although more power would certainly come in handy much of the time), and it clobbers whitetails.

The .30-06 is a classic round, and it's proven its worth many times over.