considering factory ammo in the .30-06 is more available in every mom and pop store and comes in more weights than a .270, your best bet is the
.30-06 You will carry more lead downrange, meaning a "possibly more efficient kill", I stress possibly, because if you cant hit the vitals, it doesn't matter if its a .50 cal , you need a gun that fits your body first and foremost, and thats comfortable to shoot. Nothing wrong with a .270 at all, its just that with 150 grain bullets being your max for caliber, they better be premium for the bigger moose/elk or they may fall short of maximizing a quick ethical kill. This is just from my personal experience, and I know MANY MANY people have taken lots of big game with a .270 I prefer a larger bullet so that the impact and penetration are a little more substantial. Several of my friends have complained to me that their 270's made a wound on the way in, but no exit wound, so the animal thats not hit in the vitals will bleed a lot less with one hole (and sometimes if there is only one hole, the skin moves to cover the entry wound hole and limits blood loss, resulting in a longer chase and recovery of a wounded animal)