When we were looking for a sister for Crosley, we had the choice of two females. One was very energetic and running around nipping our fingers and real feisty!
Wrigley was the shy one! She came to us, but she was calm and laid back, so was her brother that was there. They had the same exact personality!
It worked out good for Crosley because she was 4 1/2 years older and didn't have to deal with a really rambunctious, annoying little sister!
Having said that, Wrigley is still very shy. She's shy around people and other dogs and she's 2 1/2 years old.
So it really does depend what you are looking for and what fits in best with your family!