I'm not sure if there's every been a list of the most fragrant. In my garden, it's Marc Alan Carpenter.

H. Citrina
H. flava
H. var. 'Hyperion'

any others? An old variety called Fair Child is in our church cemetery and the 3 clumps are quite fragrant!

Techny Peace is the most fragrant one I grow.

Hyperion Elite is a big yellow tet with that classic daylily fragrance. Klehm introduced it but it not listed in their on-line catalog. I keep it for its fragrance. It often sells when a guest inquires about it.