Well actually, they're really about the same (they've moved around the same number of album equivalents: 27Mish). But considering Katy's career has been shorter, I'd say hers is more impressive, though Kelly is more respected.
Kelly, easily. Katy is a singles' artist, not that there's anything wrong with that, but Kelly is the complete package and has sold far more albums and is far more acclaimed and beloved
Kelly also made Katy's main producers relevant, so basically no Kelly = No Katy
