IMO the most likely is Pagan (well ... non-Abrahamic) given that there's to few Republics (Genoa, Venice, Pisa, Ancona, Bologna and Cordoba ... any others?) to be 'as big or bigger than SoI' and the same deal is largely true for Theocracy (the different popes and the assorted prince bishops in Germany and Northern Italy).
Pagan on the other hand 'just' need a bit of padding and prehaps a couple of special CB's focusing more on raiding than conquering ... say, gaining twice or trice the ammount of gold from winning sieges and gaining cash by getting the opponent to surrender
Pagan on the other hand 'just' need a bit of padding and prehaps a couple of special CB's focusing more on raiding than conquering ... say, gaining twice or trice the ammount of gold from winning sieges and gaining cash by getting the opponent to surrender