Tbh, Katy belongs on neither list. Her influences are all people like Gwen Stefani, Alanis Morrisette and Joni Mitchell. She idolises Beyoncé but there's absolutely 0 influence present in the music and her opinion of Britney is nothing more than general polite PR praise.
If she *has* to be on a list, it'd be Britneys as Toxic is the reason Katy worked with Bloodshy for 'Love Me'.
The lists posted here makes me lean towards voting Beyoncé.