i dont own either. i own a 270 winchester (not wsm), and a 300 wsm. if i had to choose between the 7mm mag and 270 wsm, i would go with the 7mm mag. bullet selection, factory ammo selection, used brass availability, and performance are all in the 7mm's favor.
while i like my 300 wsm, it is no 300 win mag likewise, the 270 wsm is no 7mm mag!