Blackbeard, or hopefully, Shanks, whom i will put as my favorite character of this show if he turns out to be a shady figure.
Imu would be insanely boring, and i can't see Akainu being up there to compete with EOS Luffy in terms of strength, when the likes of Kaido are set to fall before the end game. Then again Shanks shouldn't logically be that strong either, i am just hoping for a solid twist.