What are the intended uses?
It all comes down to the intended uses.
If it will be for more of what you were doing before, it's really hard to come up with something as versatile as the 30-06.
Changing to a shorter (308, 250-3000, 257 Rbts) cartridge can give you problems with the length of the magazine and the shape of the mag follower and the feed rails. Keeping to a cartridge of the same basic length and shape make things easier.
This means stuff like 25-06, 6.5-06, 270Win, 280Rem (7mm-06), 338-06, 35 Whelen, and then some serious wildcats that are just plain wicked.
Don't count out all the Ackley Improved type cartridges either.
Me personnally? I'd opt for the 35 Whelen.
Unkel Gilbey