I think when people answer the "best cartridge" question the reason they invariably leave out the 30-06 is because the 30-06 really isn't best at any one specific thing. For instance the 25-06 would be a better antelope cartridge. Or the 338 Win mag a better elk and moose cartridge. Or the 375H&H a better grizzly bear cartridge. Although the 30-06 will certainly get the job done in any of these circumstances.

IMO, the 30-06 ranks as the absolute "best" one cartridge to do everything cartridge.

That is why I bought my son a 30-06. It will do everything he will likely ever ask of it to do. If he needs (wants) a larger or smaller cartridge aimed at specific sized animals that he may hunt in the future I figure he can buy it himself if he can afford an elk, moose, sheep, what ever hunt. If a person is to have only one rifle it should be chambered in 30-06. Nothing else will fill the one rifle hunter as well as a rifle chambered in 30-06.