You should move this to the poll section.
I say Katy. She's 100% live (I don't know about you all but that's a big thing for me when I'm seeing a live show), her opening act(s) is/are decent, & I've heard nothing but good things about it. I would probably personally dislike it but I can see why so many others would love it.
Britney would put on an entertaining show, but I don't know how you would feel about her tbh. I wouldn't like that she doesn't sing all the time. Nicki doesn't seem to be amazing live, I hope you make it through Super Bass okay. She's very hit & miss, but Nicki is only on for a little while so I think she's passable this time around. I've heard mixed things about the Femme Fatale tour. More praise sometimes to be going to California Dreams.