Do you reload? Lapua just started making WSM brass recently, adg makes great brass for it as well. PRC really likes the 26 inch barrels so if you want a 20, WSM doesnt lose out on nearly as much. In a 20 inch barrel I wouldn't be surprised if the WSM actually outperforms the PRC, if not it would be really close since faster powders are used in it like 4831, varget, etc. The PRC will probably want the slower burners like H1000 and the like, of which you will never get a full burn in such a short barrel. 22 inch is a bit better but wanting a short rifle you'd be best off with the WSM or even a 30-06 which would be slower than a PRC but not by much, plus great factory ammo support.
If it were me, I'd choose the WSM. But 20" barrel would just about rule out anything magnum outside of a WSM or similar efficient magnums IMO
PS: if you go WSM, get a long action, not a short action. Then you can seat long bullets out further and still eject loaded rounds if you go on a hunt and don't see anything. Then if down the road you decide you didn't like the WSM you can easily just swap barrels for a PRC, Nosler, win mag, etc etc. Swamplord has some pics you can find of long throated WSM's with I think berger 215's or something in that range. And get a 9 or 10 twist if you want to reload for the heavies like 212 Barnes bore rider (which doesn't need a custom throat) or 215 bergers (which would prefer a long throat) and stick with a 10 twist if you want to shoot 150's through 190's regularly. I wouldn't bother with anything slower than 10 personally