Katy Perry. Taylor Swift had snatched the best-selling digital track artist title, though, and will probably do it again if her next era goes well, so she is also a big threat to Rihanna.
Ciara from this list I guess if we're talking about her personal life. If we're talking commercially, NONE. Rih can't touch Bey and the other girls can't touch Rih
Ciara. Rihanna will never be on Beyonce's level. Her career is a struggle outside of the singles success. Bey's serfboard tragedy still better than 95% of her performances.