Selena Gomez, Ciara

Beyonce has been the same since 2013
EDIT: because she has no room to improve really

She has improved tho

She must not have seen her BMA performance a few years back.

both of their vocals have improved

Florence because she was literally perfect in her debut, and is still perfect today

Jessie J
Ciara

Uhmm, did you not see Ciara go from "1, 2 Step" to "Gimme Dat?" Her dancing is top notch.

And her latest video is her best, visually.

Liz Phair
Nickelback
Maroon 5

Janet has improved in every single aspect except vocals. This does not detract from her ability to serve the bops.

I was thinking of her singing, she's obviously the best at dancing.

Idk, both Selena and Ciara may have improved, but not by a lot or enough that they'd be considered decent vocalists. Can someone prove me wrong?

Demi has gotten worse imo. The style of music she's trying to do is just too generic and mindless. For someone with such a dramatic personal life but putting out stuff like Cool For the Summer... there's just a disconnect there.
Alicia Keys (vocally) has gotten progressively worse. She peaked with Diary of Alicia Keys
I can't think of anyone else that's gotten worse

oh wait. NICKI. She hasn't gotten worse but she hasn't gotten better either. I still think she's capable of making a more cohesive album than she has yet

Christina Aguilera.

katy

Also, Britney's music has gotten worse over time too, but I'm sure we all know that.

To go from In the Zone to Britney Jean is really tragic.

demi

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Anyway, I think rappers are typically examples of early artistic/talent peaks then declining as time passes. Like Jay is a great example -- he started out as good as it gets for a rapper; everything he did after Reasonable Doubt either at best just matched what he did on the first effort -- he never improved upon that at all. I don't think that's necessarily a bad thing tho in some cases.

Her 6th Grammy win this year says otherwise.

Britney/Xtina both peaked really early as far as their music/talent went. So they are the obvious choices.