Given the current state of ammunition availability I'd go with a 30-06, with a 270 close behind.
I'm a huge 280/280AI fan, but haven't seen any of that ammo on the shelf for a really long time and the same goes for the suitable magnum cartridges.
I wouldn't go smaller than a 6.5mm bore for elk unless you are certain that you can place the bullet in the proper location.
Now if you handload, the options open up significantly.
