Well, I personally go for stages with good top blast zones, and/or with platforms. So Battlefield, FD, Pokemon Stadium 2, and Small Battlefield.
My first reasoning is that a lot of Joker's kill confirms KO off the top. Just to name a few examples: First hit-Fair + Up air, First hit-Fair + Up Smash, First hit-Fair+ Up Air drag down+ Up Smash, Dair(Arsène)+Up Smash, Dair(Arsène)+ Up Air, Down Throw+ Up Air(If opponent DI's in.) He does have a decent amount that kills off the side like Fhit Fair+ Bair, Dair(Arsene) + Bair, Fhit Fair+ Up-Air drag down+ Down Smash. That coupled with Bair edgeguards also make side kills good as well.
A counterpoint to these could be platforms can mess up some of the confirms, but I've found it worth it for my second reasoning.
My second reason I've found it easier to catch landings with an Up-Tilt when standing under platforms as some opponents will anticipate you jumping for an Up-Air and throw out a hitbox or air dodge.
Third reason is it makes Joker's Up Throw more useful than it already is and adds more possibilities to what you can do. Whether it be a drag down onto the platform followed by a Forward Tilt or another grab. It does give opponents the opportunity to tech when using Down Throw sometimes, which if wanting a tech chase could be beneficial.
I just base what stage I choose on who I'm playing against and their character, combined with who I'm playing.