Who is the better artist: gaga, spears, or aguilera?

I personally lOVE lady gaga at the moment because she's so talented and has an amazing voice but she is kinda freaky and has stupid political views. I want you to choose based on their career span not just atm so I'm going to have to say Britney spears! She's had a more major impact on pop culture than gaga even tho shes catching up on her and spears career has lasted for more than a decade and she's sold 100+ million albums or pretty close to it. Christina aguilera is talented and has an amazing voice compared to the other two but hasn't had that much of an impact lol. Answer this with detail. Support your answer. It's spears for me!!