RE: 300 WSM and 300 Win Mag.
Moose are not hard to put down. More moose are killed every year with .308 wins and .30-06 rifles than all the magnums put together. My choice would be a .300 win mag for the extra velocity should you ever hunt elk which would likely give you a longer shot and tougher animal to anchor. It also leaves the option of using 200 gr bullets if ever you want to at better velocioties than a WSM. A .270 and a .300 mag is an excellent arsenal.