I think we can unanimously agree that Supernatural, Crazy Kids, Thinking Of You or Last Goodbye
are the ideal singles to choose from. I'm pretty sure ToY would be a bad choice, though

It's a bop and what not, but if she couldn't perform C'Mon, ToY would be a disaster. And it's not
viral or catchy enough so it'd clearly need a lot of promo, including a video and stuff like that.
Supernatural is PERFECT for the radio trends right now, and it goes above and beyond basic pop IMO.
Crazy Kids is traditional Ke$ha with a new twist that will easily get people talking.
Last Goodbye would be a huge shock but people would definitely love it.