My fave is Xtina. My second fave is Beyonce and someone already posted a pic of them together so i'll go w/ my third fave: Rihanna.
Xtina was seen singing along to Rihannas song What's My Name on The Voice auditions by people who attended the auditions in the audience, she chose Only Girl as one of the Battle Round songs and she even mentioned how much she loves Rated R in an interview. (P.S. Her son is also a fan)
How is that picture relevant? It was to promote their albums.
And no you're the one with the wrong info. Leona was opening for Xtina's summer tour. Xtina may have flopped but that doesn't mean she would ever open for an even bigger flop.