I mean, I "want" it to be Shanks out of pure bias and speculation, but logic for now dictates that the WG is the endgame, unless BB or Shanks invoke some larger plan beyond it, thats pretty much it. Imu is the safest guess.
I disagree. People now maybe say this because we are in Imu related chapters. But maybe when we will be in "Man with Burned Scar" related chapters,in the same poll people will vote for him. If Xebec really appears (i think you dont introduce a legendary figure like that and make it a lame or absent character,so we'll see what Oda has in store about that) people will vote for him.
Right now i think the story tells us that Blackbeard is the no.1 pirate,he has the darkness theme which is already a pretty simple symbolism about what a "final villain" is,but now also contrasts with Luffy's "dawn" theme.
Its true that Imu killing Cobra is something that makes Luffy willing to fight Imu (lets remember Luffy doesnt care about the world and never will,otherwise characters like the Revs or the good Marines would be pointless) but also makes Vivi and Sabo willing to avenge Cobra.
Luffy already know that Cobra died but he seemed more interested in finding Vivi that avenging Cobra. And by the way for Luffy Ace >> Cobra so Blackbeard and Akainu are more probable to be his final villains. Imu seems to be more Revolutionary Army material to me.