Even if it's Imu, Teach is far better.
The final villain being the guy who's been built since Drum Island has more impact than the guy who got introduced in Reverie.
Imu might be the main villain of Final Saga, but Teach is the main villain of One Piece.
One Piece started before Drum Island. Luffy’s very first crewmate was a victim of the World Government, and so have the majority of the rest. Only 1 crewmate at best could be said to be a victim of BB (and only tangentially so for that pet/plushie too).
The World Government has always been the main villain of One Piece, and it is now embodied in the form of Imu. They have been committing atrocities long before BB was born…and he couldn’t catch up even if he wished.
It is because of Imu that piracy itself is a crime. It is because of him that entire races and bloodlines have been oppressed, villainized or even nearly eradicated. The scholars of Ohara, the Lunarians, the Buccaneers, the Minks, etc all have no beef or business with Blackbeard.
Only 1 villain has impacted or abused the Strawhats’ various allies all over the world and
even many of their enemies too…and it’s the one that is the enemy of Joyboy too. It ain’t the fatso.