Lots of good calibers out there. For me 30-06 is a do it all. But so are others. 30-06 is easy to find ammo, lots of choices.
People will tell you about animals shot with smaller calibers and being just as dead. True. But 30-06 is alot more forgiving. No I am not advocating poor shots, which is what they say. I practice quite a bit, and have been lucky to only have taken good shots so far.
Over 30-06, cost will be an issue.
This year I bought a 45-70, which can be loaded mild to wild. Can shoot long range, if you know the range, and you round, but is not usually chosen for such. Unless you want to kill a million buffalo. But unless you load your own, expensive. Even then 30-06 i cheaper with more components on the shelf.
People have shot black bears with smaller calibers. But if you are buying a new rifle, and not utilizing an existing rifle, why go small?
7mm magnum and 300 win mag are probably popular for deer, elk, and bear rifle too.