If I could only have one .30 cal, and I was a handloader, I'd choose the 300WSM. As it is right now, for .30 cal's I own a couple 30-06's, a couple .308 Norma Mags, and the only short mag I have is a 7mm WSM. I like the WSM, and haven't noticed feeding problems. I would pick the 300 WSM because I'm a bit of a velocity junkie. If I only had one 30 cal, I wouldn't be happy with 180 grains at 2700 fps. I'd be pushing hard to get the 2800 fps or better, and, depending on the firearm, that may not be the safest thing to do. But with the WSM, if I were getting >2950 fps with 180 grainer, I'd be content. Don't ask why, because I don't really know why. I just know where I'd be happy and where I wouldn't. But, as said earlier, the fit of the gun is far more important here than the cartridge its chambered in.
Oh, and I'm sure the OP has already made his choice.