According to the Project Manager's Book of Knowledge, legitimate power is always the best way to get someone to do something.

Question

Quizplus · Accepted Answer

It really depends on the situation. We want to emphasize that part of being the project manager is using influence in intelligent ways.
Key Takeaway: Often expert power is the most effective. If people respect you and believe you know what you are talking about, you may be able to get people to do things without ever exercising formal power.

According to the Project Manager's Book of Knowledge, Legitimate Power