When purchasing plants I purchase stock plants. If they look healthy. I do buy certain varities of veggies and flowers.
When purchasing seeds I do purchase brand names, have noticed a difference in their germination.
Most of my daylilies have been purchased through Gilbert Wild and Sons. I would rather purchase root stocks, (hostas, daylilies, peonies, iris's) through mail order companies. You get a better root stock. I've had better success with bare root plants, when purchased through reputable companies.