IMHO, they're all usable. I prefer the PRC. Multiple good brass options and other average brass options too. A reasonable amount of factory ammo options are manufactured too. Factory ammo is readily available. Maybe not during the current crisis but at least they're on the roster. No fire forming or necking down. It isn't magical but neither are the other two options you listed but it's convenient and checks all the boxes for me. The short action (with extended box mag) and 24" barrel combo seems to be a sweet spot that is tough to beat for weight, mobility and efficiency. The ballistic performance to recoil ratio is phenomenal with these cartridges.
Brass options and availability for the 6.5 WM leave plenty to be desired. Plus it seems as if you want to take advantage of the higher capacity case and longer burn column, longer barrels make it shine. And of course a long action is the only option. Not a problem if you don't care but personally, I prefer a SA where possible. No real factory rifle options. Little to no factory ammo options.
6.5 SAUM. It was the best thing going for a short fat case until the other contender came out in the same class. But it's still a wildcat with limited brass options unless you want no neck down. No real options for rifles or ammo.
A lot of guys hate the PRC because it's nothing new because there were already options available. IMO, the concepts of them were great but the execution of them for the average shooter was a fail and flop. Hornady came up with a comparable offering with factory ammo options and factory rifles chambered. They developed the sweet spots for loads and produce all of the above. When things are available, you can go buy a factory rifle, scope, rail, rings and a few ammo options and you will likely have a fairly decent setup with minimal work in the same day. Not quite a turn key arrangement but a lot more turn key than the others. Complain all you want but Hornady did a good job. It may not offer any ballistic advantage compared to the other two but they did the whole package from A-Z in a pretty attractive package. If you thumb your nose at Hornady for marketing ploys, then by all means, go with the WM