Is Thanos better than the Joker?
Comics wise,
the Joker wins hands down. So far only one person has played Thanos. His portrayal of Thanos was amazing. However if you consider the best acting as the Joker, Heath Ledger, then Brolin portrayed Thanos so much better.
Can the Joker beat Superman?
Though Joker is almost always a Batman villain, he has actually beaten the Man of Steel several times. Despite this, DC has proven that
the Joker can actually beat Superman, even without powers. In the popular Injustice storyline, Joker managed to completely break superman after tricking him into killing Lois Lane.