Great Mosque of Djenne >> Hagia Sophia.
Why?
If you're playing a religious game (which I recommend every time, the bonuses religion gives can make or break a game), you'll want to spread it as far as you can. This means investment in missionaries, and the GMoD essential increases your missionaries worth by 50%.
Also, GMoD gives more faith than HS due to the fact you get a free Mosque. Since BNW, the AI have prioritised taking faith buildings in their religions, hence getting more than one faith building in your religion needs a damn load of luck. The fact you are not likely to be getting Mosques, getting the bonuses of a Mosque at that stage of the game is pretty powerful, particularly in faith generation.
If you were to take the +2 tourism per religious building reformation belief, you could potentially have three types of religious building in one city (+6 tourism), which is a great head start vs AI.