Knockout... is one that I don't recommend to anybody to buy. It's one of the worst hostas on the market IMHO. Absolutely ugly at mid season...and worse at season's end.
Komodo Dragon
Korean Snow
Krossa Cream Edge
Krossa Regal...an old classic... stunning at maturity. Large vase-shaped mound can be the center of attraction for a shady bed. This slug-free hosta will reach 36"high x 71"wide at maturity. Exceptionally 6 to 7 feet long stalks with lavendar flowers.