They are not similar, Katy Perry just did an album that it is exactly like Animal. I'm not a fan of neither but I choose Ke$ha because she actually has like 3 or 4 good songs on her album, Katy only has 1
I think Katy tends to follow what's popular more than being a leader whereas Kesha does more her own thing. I don't love either of them but I listen to both their music. I suppose I'd go with Katy, mostly on the fact she's had 2 albums so more songs I like