The 30-06 is about as well balanced as they get. Wide bullet selection, great shape for feeding, long neck for cast bullets. Most other cartridges are more nich cratridges that do one or two jobs better, but not as a wide range.
Great cartridges: 243, 7x57, 270, 30-06, 35 Whelen, 375 H&H, all great cartridges, with out the fluff and sales hype of the supperdupers and specialty cartridges that you will not find in the small town hardware store.
Some might go a little faster with lighter bullets or carry heavier lead without the ballistics, but, the 06 will do it all in North America. I have many calibers but I will always come back to the 06.
John