Well...
Avril is irrelevant both musically and as a celebrity
Pink is doing very well with her music, but she's not a very talked about artist (which can be a good thing)
Christina is struggling to find the same success with her music as she once had, but she's talked about
Kelly gets one hit per album and gets a decent amount of media attention
So... Musically, I'd say Pink, but as far as fame goes, I'd probably go with Christina. Kelly could sneak in there too tbh but I don't know if she's done anything iconic...
Breakaway was a huge era for her, but I'm not sure if she actually got anything iconic out of it?