It's a tough choice, since they are basically the same. That being said, I purchased a 7 STW a few years ago due to the STW forum on this website. Like someone else had said, the STW is very easy to load develop and it likes just about everything. You have a ton of information available on it since the cartridge has been around for some time now, and all the STW owners are pretty passionate about the cartridge and willing to help you out if you need it. I love mine. Loved shooting it so much that I burned the barrel out in about 3 years. It's got a new carbon wrapped barrel in a 1:8 twist and shoots great. You can't go wrong with either one. Brass for the STW isn't an issue anymore, and when it was, I just necked down 8 Rem Mag brass without an issue. I will say this, the outiftter that I hunt with in Wyoming has a brother that is a gunsmith and owns a gun shop. When he asked me what rifle cartridge I was going to be using (this is the first time I hunted with him), I told him the 7 STW. He said "that's a fine cartridge, and my gunsmith/gun shop owner brother's favorite and he's used it to take game all over the world".
The gunsmith I use here, in San Antonio, actually helped Layne Simpson develop the STW cartridge years back. He loves the cartridge.