My oldest DD has done both. She has done BBB twice. Once she got the largest package, hair, nails, makeup, and an Aurora outfit. Another time we brought an outfit and she got hair, makeup and nails. BBB is more about the hair and they also do makeup and nails but the hair is the focus depending on the package you get. Pirates is more about the makeup but they also do the hair and nails but the makeup is the focus. After BBB, she left her hair up for several days both times. She got different styles each time. She only wore the dress from BBB for a few hours. She got hot. She wore the dress we brought for most of the day, but it was not a true Disney princess dress. It was more a tutu and t-shirt Cinderella inspired outfit. At pirates, we purchased the mermaid tutu and t shirt outfit, which she wore most of that day. The make-up at Pirates stayed on all day even after she got in the pool that night only the glitter came off. In fact, the makeup stayed on for part of the next day too although not as nice. I made her wash it off the next day. She didn't complain about itching with the makeup at Pirates or BBB.
Overall, my 6 year old prefers Pirates League to BBB. She thought the experience was more fun.