Any! My guess is OSM's official tile server is probably the most reliable, but I really have no idea. Since maps are currently broken on Miraheze, I'm guessing not too many wikis are actively using it. Thus, I suspect we wouldn't meet the "heavy use" that is forbidden in OSM's usage policy.
I do not know how production Kartographer works. I'm guessing you all are using Kartotherian, and the tile server is configured somewhere in there.