Pure bias: Shanks
- Is tied to the series since the beginning
- Has heavy emotional ties to the MC
- Already is doing weird shit (i.e. Gorosei)
- Has a tendancy to look super ominous at times
- Has been shown to be pretty broken and basically is just Roger at this point (even sharing attacks).
I expect Imu, because I think Shanks is going to be the defined measure of when Luffy surpasses Roger. Since Roger is dead, the next best thing is the protege, who seems to have deeper intentions for Luffy. I dont know where Blackbeard falls into this, either before or after Shanks, but I do not believe hes the final villain, nor Akainu.