Thanks for taking a look at Behavior Designer! One of the tasks that Behavior Designer includes is the Utility Selector task, which allows you to use utility theory within behavior trees. The paper that this task is based on is located here. There is a Utility Theory Sample Scene that has the agent switching between eating, sleeping, and working, all based on a utility curve. It sounds like this is similar to what you are going for Behavior trees can be used for either. The utility theory sample is similar to the former, and the Ultimate Character Controller demo tree is more similar to the latter.