To me, gaga is just on another level compared to those artists. Sure, Katy's "Roar" was #1 for however many weeks but Gaga's material just has more substance, her performances and videos are completely though out and creative, and she doesn't make music for the charts or to please anybody other than her fans and herself. i love Katy and Rihanna (not really a fan of Nicki and Ke$ha). I listen to their stuff when i just wanna listen to something fun and exciting. I listen to Gaga when I'm feeling artistic and creative and needing inspiration. Listening to Gaga is like a whole experience in and of itself!!