First of all I don't believe at all that Teach will be the final villain although the interaction of his subordinates with Saturn can give Teachtards (aka
@Erkan12 since he is the only one in the whole world) a bit of hope.
But I have to agree that having Teach as the final villain would be 1000x a better choice than fucking Imu. Why?
Teach is such a cool character and badass without being overpowered as we see him growing since the beginning of the series. He is always putting himself in dangerous fights and he is not afraid of going for what he wants. Yes he is not stupid as Luffy to go for impossible fights but he is still too fucking brave.
Now what about Imu? Well first of all Imu doesn't even look THAT strong from what we saw so far. His CoO (if he has) sucks since he couldn't sense Sabo on the same room as him. His lethality sucks since he couldn't one shot fucking Cobra (old ass regular human weaker than Vivi). His speed sucks since he allowed Sabo to escape (and he almost escaped while carrying Cobra with him). All he did was sucking some fire from Sabo's Fire Fist attack and back stabbing Sabo on the run while he was carrying Cobra.
Now let's recap Teach's feats along the series... Killed Thatch to have his dream DF for him. Then he 1v1 Ace and survived while Ace was arrested. Then he became a Shichibukai and made his master plan of breaking Impel Down and getting half of his current crew from the best prisoners that were there plus Shiryuu (forgot his role). Then he went to Marineford to kill Whitebeard (failed but disease helped him) and got his DF. Then he fought Marco and WB remainers getting control over their territory and becoming a Yonko. Then he convinced an Ex-Admiral to join his crew. This man is a beast. Just a reminder that while he was doing all that Big Mom was fucking waiting to have the perfect marriage for her kids, Kaido was fucking waiting to have an army of gifters. Shanks was fucking waiting Loda knows who or what.
Now let's recap Imu's feats along the series... Made some stuff 800 years ago during Void Century. Then he hid himself for 800 years and played with Gorosei of being the King of the World although he couldn't get out of his room (maybe 800 years grounded?).
That's the truth.
For those reasons having a badass character like Teach would be 1000x better as a final villain than a grounded child character as Imu playing as King of the World with his Gorosei babysitters.