I love Rihanna, but Aaliyah was the better singer, the better dancer, the better performer and the better actress.
EDIT : Reading these comments, Aaliyah's vocals seem to be pretty underrated. Her extremely low notes ('Are You That Somebody', 'Death of a Player'), her runs/ riffs and her head voice >>>>>>>>>>>>>>>>> careers
Keep in mind that Rihanna has been improving year after year after year while Aaliyah didn't have time to perfect her craft.
Unfair comparison to both artists!
Aaliyah when you compare her to Rihanna's early work.
Rihanna now.