My first moose ever was with a .270 - I still have the same rifle (that was 22 years ago). I now use a 7mm Rem Mag for Moose, but my backup is my trusty .270.
I used a .280 Remington for a few years and had good success but cost of shells in relation to the .270 was the difference.
Many guys I've gone hunting with swear by their .30-06 and I would agree it's a fine rifle. It really comes down to preference.
Where I grew up (in Northern BC) many of the First Nations hunters would use a .30-30 and take moose on a regular basis (not much different than a bow).
If you're looking for a gun that'll take a moose on a flat open field a .270, .280, 7mm can't be beat based on speed of round (provided there's a heavy enough bullet - 170gr is what I shoot), but in densely wooded areas, you'll want to go to a heavier, slower travelling bullet.
It's funny - everyone has a caliber that's their favourite, but in reality, a .270 or greater is enough to take a moose provided the shooter is competent and can put it into the kill zone at the right range.