1) Bowie - duh
2) MJ - ignoring the obvious, he's the greatest popstar after Elvis and Madonna
3) Beyonce - no one has come close in the 21st century. Great singer, dancer, performer, probably the most political of the bunch, and has spanned genres.
4) ABBA - obviously fantastic pop music and Eurovision legends, but Mamma Mia! really did a number on how much I enjoy listening to them
5) Mariah Carey - probably the one whose discography I know the least of, but insanely talented back in the day, a meme queen, and the more I learn of her music the more I enjoy. Fantasy > Britney's entire career, alone.
6) Whitney Houston - I know she was huge in the 80s and early 90s but I really have to be in the mood for her. The self-destruction kinda taints her in my eyes, too; I know it's tragic and everything but I sometimes can't look past how she fizzled out.
7) Britney - just... nowhere near as talented or interesting. The rest are hard to place because of their legacy but hers is just the work of great producers.