I would go with Gauguin. It is more of a aHHHH plant than Black Pirate. Black Pirate is not as black as Black Panther and holds its foliage more upright. But as most dark reds unless it is sighted so that you can see the petals lit from behind by the sun you would need to be close to really enjoy the plant. Black Pirate's foliage is more appealing but I have noticed attendency for the flowering stem to become ratty during the summer. Gaugiun's flowers like many of the blends will vary from year to year. But all peonies vary somewhat each season because growing conditions.

Either one you will have a treat.