No method is best in general; a method is best for a goal. The lecture suits organised presentation to a large group, discussion suits judgement, and demonstration suits skills. The exam question is almost always: given this goal, which method fits?
Worked example: learners must generate many possible solutions to an open problem, such as reducing waste in a college canteen. A lecture would give them the teacher's answers, not their own. Brainstorming fits: ideas are generated first without judgement, and only afterwards evaluated. Judging too early kills the method, because learners stop offering unusual ideas.