Born this Way, easily, although Fame Monster is excellent. There's only a handful of good songs on the debut.
Madonna is great, but I find Gaga much more interesting. I don't see the Christina Aguilera thing at all, aside from "female pop artist of the 2000s."
I don't know the third person you're comparing her too, but I don't think Lady Gaga ever claimed to be the first weird costumed pop star, and the look of Gaga's body has no effect on the quality of her music whatsoever, so I'm not sure why that's even being taken into consideration. That said, she's way the fuck more attractive than 90% of her fellow pop stars.