I often think in deer vs elk terms due to living in the Colorado mountains I suppose. I'd pick the 7MM-08 for whitetail, the 7MM Mag for elk.
7MM Mag is very easy to find, not sure about the 7MM-08. May differ from region to region.
Just bought some ammo for my 7MM STW...speaking of ammo availability. The counter guy at Big R acted like he had not heard of the round in quite some time. Which is quite believable. Why some rounds take off while others do not is a subject of endless interest.