Britney is enjoyable and fun as ****, I love her. But Gaga is sort of deeper, I am not saying that her songs are serious and artistic, but I don't know, her music is more intelligent and you feel it more than Britney's.
But I don't know if they are comparable, Gaga is currently working in her fourth album and Britney already has 7 albums

. And in my opinion, Gaga's discography is coming stronger and more groundbreaking than Britney's.
And Circus is such a ****** album. I wish she didn't release it.