Which Edition should I choose?

The main reason why companies choose a group license like the Pro or Business Edition is for security reasons: E.g. If an employee leaves the company the MindMeister license admin is able to disable the MindMeister account and transfer the license to another employee.

The Business Edition is the right choice if you want to establish collaborative relationships with your clients; it enables you to automatically turn other users into Pro users by just sharing a map with them.