Disadvantages of the WSM: Ammo availability, and higher price.

Advantages of the WSM: higher velocity than the standard 270 equals slightly flatter trajectory (only 1" at 300 yards, but it increases from there).

For most folks there isn't much difference since shots will rarely be over 300 yards. Bottom line, if the availability of ammo doesn't bother you and you like short action guns the WSM might be the way to go. However, if you need to be able to buy ammo wherever bullets are sold, and the short action gun doesn't matter to you, get the 270 Win. and you'll have one of the classic calibers.

Gordon