Selena. Demi's got a better voice and while none of Selenas songs are as good as Skyscraper I prefer Selena's music overall and I think she's a better actress. I prefer Selena as a person too.
And you make money by making great songs and being likable, which is why Selena is the bigger success.
The thread is not "who is more successful?" It's who do you prefer. I prefer Demi's voice to Selena. Even though I like a few Selena songs. And yes, I agree with your point that she is likable and her singles are really catchy.