I enjoy playing as America and China, and back before Brazil, the Inca were (and still are) incredible.
For europe I go as rome, greece or England. In africa/middle east I sometimes play Songhai and arabia.
I also customized a TSL map to make Venice start in Australia. I didn't play as them but the result was incredible.
Venice had the largest science output in the medieval era and had annexed ALL the city states on the Swahili Coast, and had practically wiped out the Zulu's except from one city, nobamba, which was landlocked within the venetian-south african kingdom.