The best is naturally accumulated.human-centered.intuitively designed.made by experts.input-driven.behaviourally grounded.real work.validated by humans.native to its context.right in front of you.right in front of you.
The best AI learns by example. Training data is those examples: records of a task done, and done well, that an AI studies until it can do the task itself. The closer the examples are to the real job, the better it gets at that job.