Depends on how high of keys you do realistically. For 10-14 Disc and Holy are pretty similar as far as how often they show up. 15+ is when Holy priests start seeing a decline, and disc becomes more of an obvious choice. At 20+ Holy is basically non existent.
https://raider.io/mythic-plus/season...MythicLevel=14
https://raider.io/mythic-plus/season...MythicLevel=99
https://raider.io/mythic-plus/season...MythicLevel=99