DC has stated that The Joker respects at least one villain, The Riddler. Joker and Riddler are regular Batman opponents who often clash with each other. While they frequently agree,
they've often clashed. Tom King's Batman "War of Jokes and Riddles" storyline is significant. The Joker and The Riddler forged an alliance against Batman in his second year,
but their dispute over who should murder him leads to a gang war. This storyline showed how two egomaniacs can't coexist for a single purpose. One respects the other.
Red Light, Green Light is a tale in Batman #15 by Scott Snyder Greg Capullo, Jonathan Glapion, and James Tynion IV. The Joker encourages The Riddler to flee Arkham Asylum before a Joker Bomb kills him
The Joker thinks The Riddler understands the greater picture of torturing Batman better than others.
Joker knows that he and The Riddler are alike. Both are sociopaths with Batman obsessions beyond killing or defeating him. These villains would rather fight Batman