Azula. There’s this great video of her voice actress cussing in an Azula voice, and it honestly doesn’t sound that weird and jarring.

I've seen it, funny as hell

My personal opinion, I go with either Toph, Sokka or Korra. Toph is self explanatory, Sokka would just be funny and Korra's VA has and sounds kinda natural.

They weren’t included here but I think Mai and Katara would probably swear the most if this weren’t a kids show.

Almost all of these characters wouldn't swear due to professionalism and Sokka... is Sokka. I would say Korra as she is in the least formal position and she's at an age and time period where swearing is most appropriate for someone with her demeanor.

I might go with either Azula or Toph

And MAYBE zuko

Toph because she wants to be rebellious

It would be funny if she kept cursing and Katara yelled at her every time

Toph would let it rip

Korra would only do it if she angry like Vi from arcane

Sokka would do it on occasion

Zuko would rarely sully his words

Asami would never

Azula would be the most constructive with it

Definitely Toph.