Above all, Joker needs to be funny. Joaquin's portrayal, while well acted, was more piteous than funny. I actually enjoyed Leto's sick sense of humor and thought he was one of the more redeeming qualities of Suicide Squad. Joker is the better film though.
Another "hot take," both Ben Affleck and Jared Leto should've continued their roles in the DCU. Batffleck was actually pretty great. He's perfect as flip billionaire Bruce Wayne (and has the best bat suit since Adam West). Bruce's public persona is an act and is always portrayed as too righteous. He should be kind of a dick. Will Arnett's Lego Batman Bruce Wayne is right on the money.