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
Aaliyah is better singer and clearly better dancer. Aaliyah. Aaliyah's voice was so pretty and angelic. Her tone alone was amazing. Also Rihanna does not have the range that Aaliyah had. Aaliyah had a beautiful head voice and could sing very low.
Rihanna could never do this, and Aaliyah was only a teen:
Also Aaliyah was the better actress. Acting takes talent, and Rihanna to my knowledge isn't that good of an actress lol.