Best = people! For example, as a thank you to people who help translate my work or as a form of micro-encouragement to steer positive micro-actions (e.g. tipping a great question on stacker news!) The value for money is high because for fractions of a cent, you can put a smile on people's faces and foster the type of behavior you personally want to see more of. Sats are a tool to shape the future we want to live in.

Worst = since sats are money, I'm going to cop out and say, any fiat that could have been converted into sats but I chose to spend on an overpriced drink instead, is not a good use of could-have-been-sats!! :D

Thank you for your question! <3