Gosh, I've been so indecisive.

Seeing as 5e did away with alignment restrictions, would anyone object to an evil paladin? Not an orphanage-burning, man-eating evil, but a victory-at-any-cost, ends>means evil. He could care about his mission, even the good of the party, but be a ruthless scourge to anyone he perceives as an enemy. 
He'd probably be a thrall of Beshaba or Shar; there's a sisterhood dedicated to Shar in Hulburg.