After most of the reveals have now been made - I'm pretty sure that I'm going with
Sweden first.
Sweden gives a lot of bonuses to one of my two favorite victory types (Culture, with Science being the other one) as well as bonuses to one of the main new GS game concepts (Diplomacy). It also strongly encourages wide play, which I much prefer. I think that Sweden will fit well into my normal play style, rewarding me for things that I already do - and encouraging me to focus even more heavily on some of them.
While I think that I might like Mali and Maori more. They are both certainly very interesting; however, they change a bit too much about the base game for me to start with them as my first Civ for GS.