Either will certainly do. With all of the new short magnums the .300 RCM seems to be falling to the side though and being left behind so getting ammunition could certainly be an issue in the future.
The 7mm STW made a big splash when it first came out, but it too sort of fell by the wayside for a decade or so, but has made a resurgance in the last few years whith quite a few rifles being produced in the caliber by remington particularly as well as some of the other major manufacturers.
I think the 7mm STW is back to stay so future availability of ammo is likely to be good.
If I were in your shoes with the same needs (which I am) I'd go either with the STW or 300 Rum; and I own one of each.
Of course you also should consider the 300wm and look to the 300wsm if you want to go with a short action. Both of those calibers are going to be around for a very, very long time.
For deer sized game and larger my 300 Rum is by far my favorite, but I absolutely love the 7mm STW for deer, hogs, coyotes etc and would not hesitate for a second to use it on an Elk Hunt.