"Pick one, Kiddo", would be preluded with an extensive exchange of pros and cons to assist the Kid in rendering a decision. During that process, the "choose one or the other but not both" parameter would have been conveyed as a non-negotiable. I am the parent and have the duty to place restrictions where I deem appropriate.
The child, unknowingly as she is guided through the process, gains experience in:
Managing a risk and making a decision - I have 2 options. Both have good attributes, both have bad. What are the most important things to me? Friends? Coach? Team mates? Fun? Ice time? Development? What the Coach wants from me? What are my parent's views? etc. Make a list and place a value on each item.
Taking responsibility for their decision and to fulfill their obligation - I chose this team and this team chose me. I will provide my best effort at all events, regardless of how our season goes. Team.
Aquiring a sense of accomplishment - I made that decision. I did what I said I would do. Another kid got to play competitive. I feel good about me.