After playing every civ and every leader here's where I'm at. Your mileage may vary. I think the biggest surprise for me was the Mughals. When I first read the design for them I was underwhelmed, but they are so strong it's ridiculous. It's really hard for me to justify not picking them if they are available. Very sad about Pachacuti and the Incas as they were my favorites in Civ6. Also, Maya should really be in its own tier of S+, absolutely broken.