Most fragrant for just one plant would be Lexington, Hyperion, and Hudson Valley. Spanish Fandango has only been here two years and I haven't noticed the fragrance yet. For a mass planting there are two: Miss Amelia, a small flowered DL--there are 24 plants in this group. Then there is Imperial Lemon which is my favorite yellow DL. We do have four plants of Chance Encounter but have not noticed a great deal of fragrance. I believe most fragrance seems to come from the yellow daylilies, so would be interested to hear from others about this.
Miss Amelia
Hudson Valley
Imperial Lemon
Hyperion