Ke$ha can always hold her audience's attention. Obviously some you haven't seen her tour performances. She's not like Mariah who just stands there and doesn't interact with the audience at all.
Ke$ha is great live, I just saw her and she turned the whole place into a big party. What she does on stage with her choreo and dancers had everyone fascinated.
I'd say Carly Rae Jepsen, what I've seen from her she always seems very awkward on stage.