My preference in a daylily is one that opens well, has good foliage, and resist thrip damage.
I personally dislike treating any daylilies for any type of disease, "I don't live in the rust belt" which is another thread all in itself.
I'm looking at bud count, the more the better, but not so many that the blooms mash into each other so that can't open properly, well spaced branching, on scape's tall enough to properly display the blooms, I also prefer pod & pollen fertile, but if it's a good garden plant I can live with it if it isn't.
I need a good cold climate hardy plant here in NE WI
A good robust plant that can handle a little diversity without going into a funk that causes it to shrink or not bloom the next year.
Now we look at the bloom itself, is it pretty? open well? is it something that you like? are the colors pure and crisp? how long of a time period does it bloom? I had some beauties that flamed out in a week, pretty mass of blooms, but not a good garden plant.
When I look at my seedlings after second bloom year I think to myself "would I buy that?" or even better "would I be willing to sell that?" if I tell myself yes I know I have a winner.
seedling pic's some new, some old