Xtina. All the vocal tools are there, but she has seemingly forgotten what technique, restraint, and subtlety are, unfortunately.
This. Christina is massively overrated as a vocalist.
EDIT: I don't see how Beyoncé can be overrated. She's a great vocal technician. Is she a great phraser and emoter? No. But, her vocal technique is amazing and she knows her instrument unlike the artist I mentioned above.
'I don't consider that type of obnoxious screaming to be talented singing and she can barely hit a note'
I'm providing reasoning (aka the opinion) behind my choice. Like how they tell you to "explain" test answers in school, which is something many here should still be familiar with.