Between Broly and Buu. Depends on how much you consider Insanity evil. I go with Buu because he does kill people in strange ways.

Excluding Buu and Broly, since they're obvious, the third evil is Bojack.

I'd put Dabura at third. He's a Demon, and we now some of the stuff he did.

Buu is the most evil I misclicked

Dabura went to Heaven after dying, because the only evil things he did were while under Babidi's control.

Cooler or Bojack get my vote for most evil discounting Broly and Buu, but Buu is literally made of evil.