I voted for Black Panther. Like GoTG it would open up a whole new world for the MCU. Wakanda itself will be glorious to behold with it's mix of tribal and high-tech culture. I really look forward to seeing that world brought to life, not to say the least about the character and his supporting characters and enemies.
My choices for T'Challa are: Chadwick Boseman, Aldis Hodge, and Blessing Mokogohloa (from Spartacus War of the Damned). I always wanted Djimon Honsou, but now that he's in GoTG that won't be happening. I'd love to see Kevin Greivoux as Man-Ape.