I’m a bit late but I’ll of course shill for my own guild first and foremost, Shadowed Star. We’re a Forsaken military RP guild with very heavy Shadow and populist themes. We’re a good fit for most Shadow Priests in my unbiased opinion.
https://us.forums.blizzard.com/en/wow/t/h-rp-shadowed-star-undead-death-knight-military-rp-guild/548637
I will also say that I am familiar with RAS and I think they’re a fine guild as well.