I always thought that some of the civs with the biggest sinergy with Tabarnak's 4 cities Tradition Opener are the Netherlands (also remember that, with protecionism, it is 4 happiness per luxury resource traded away and 6 for the non-traded!) and Rome (easier to build the libraries, the granaries, the shrines...). I also thought of another one, but I suddenly can't remember...
EDIT: Remembered! IMO, Ethiopia, because you would get 4 free Steles.