Those are the two best all around big game calibers for North America and especially for Elk. I’d give the edge to the .300 win because of the larger caliber slug and slightly better ballistics but honestly you’ll be just fine with either. I own both, have killed elk with both, and have complete confidence in both to get it done.
I’ve kind of settled on the .300 for elk however and the 7mm for deer. I just like the .30 caliber for an Elk and the added knock down power since elk are quite a bit larger animal than a mule deer.