In DC I don't know who is worse than joker
prehaps Darksiders with his omega beams can put people through infinite death were each death is worse than the last (essentially golden experience requiem) but in other stories here are some characters who I think are more evil
The gravemind (halo) - wants to infect everyone with the flood which living as an flood infected is the worst thing I can think of. were even after your body dies your soul will be constantly expirencing infection inside neral physics you will essentially be living through immortal life of being infected and violentenly mutated by the flood for all of eternity and that's is as far I'm willing to explain living as a flood infected without extreme sickoning detail as the gravemind does this by choice to torture the forerunners for the precursor genocide and for fun.
Griffith (beserk) - will rape his best friends girlfriend in front of him just to tourment him, will wipe out his friends, family, kingdom and the human race just to become a god hand, pushed guts to his lowest point where he attempts to rape Kaska and bits off her one of her breasts, cuts off the limbs of horses and watches them squirm in pain until they die if blood loss, rapes and impregnates women with his demonic children, ect
Frieza (dragon ball) - Frieza sees genocide as beautiful as fireworks, laughs at the multiverse even his universe being erased, will disable the limbs of his soldiers and watch them wiggle on the ground like a worm in pain for fun, murders and enslaves children, toutures those who are merciful, laughs at people suffocating in the vacuum of space (which is the most painful way to die), genocides entire civilizations and sells their planets to the highest bidder only to re conquer the world later, ect
And I'm going to stop typing now so this isn't an infinitly long post full of other evil characters or more of how evil Frieza or Griffith is