It`s logical if you`re most fave artist is a pop singer he/she to come to your mind, so Gaga!
But as a whole - all of the pop divas - Gaga, Brit, Riri, Katy, Beyonce, etc.
From all that you mentioned, Brit is truly the only one that stayed true to her roots and what she does best... Pop!!!
Gaga = pop then rock
RiRi = dance, urban and slight pop
Katy = urban with first single from second album, but for most roast, pop
Beyonce = mostly urban and perhaps some slight pop, though I can't recall any singles or sings being Pure Pop