There were many lingua francas of which French was supposedly the first global lingua franca. That changed and it became English (from what I understand). We will probably see another language become the lingua franca, so my question is: should it be English? Are there better candidates out there? Why / why not?
English if we want ease of communication (and is the most likely path forward)
Esperanto if the goal is to teach it to a whole generation: it is designed to be easy to understand when you already know one European language (especially a latin one I think?)
Chinese if the goal is to speak the language of the dominant non European power in the next century