Thanks for asking. There is no best one, but there is a right one. That will be based on your product, market adoption, users, and your mission.
Few pointers always help:
- focus on value vs features
- will your mom understand it? (B2C generic product) are you selling to right people - solve for control for CEOs (dashboards), cost for CFOs, save time for accountants (Xero)?
One good way to start with is ask your users, “How would you define X to your friend?”
You can iterate from there. April Dunford’s book, Obviously Awesome, is a good starting point. She also has some good tweetstorms on it, one it this: https://twitter.com/aprildunford/status/124252626722172518559