A little history.
Winchester planned to introduce the 300, 270, and 7mm WSM at the same time. Shortly before putting them on the market however, they discovered that it was possible to load and fire 270 WSM in a 7mm WSM chamber. This was a dangerous situation, so they delayed introducing the 7mm for a few months to tweak the cartridge design slightly to prevent this.
The 7mm WSM was arguably the best of the bunch but was late to the party. By the time it was on the market everyone who wanted a WSM had a 300 or 270 WSM. The 7mm WSM has never been popular at all.
Then Rick Jamison sued Winchester. Jamison developed the idea for the WSM cartridges and Winchester stole his idea. He sued, won and Winchester, or anyone else making rifles or ammo in the WSM cartridges had to pay him a royalty. I think that has expired by now or will soon.
The ONLY reason the SAUM cartridges, or the Ruger short action magnum cartridges existed in the 1st place was to work around having to pay the royalties. The WSM cartridges were always better, but due to the lawsuit would be less profitable for manufacturers.
I don't see a bright future for either cartridge. Brass availability would be the deciding factor for me. You can always make 7mm WSM cases from much more readily available 300 or 270 WSM cases so I'd lean toward 7mm WSM based on that.
Personally I'd go 280 AI and call it good. The difference in long action vs short action isn't that big of a deal. Having 5+1 vs 3+1 capacity is more important to me than short vs long action. If short action were a must, then 7-08 will kill stuff farther than most people can shoot.