If you choose any of these options, you do not have to choose to do things entirely one way for everyone in your organization. Which mix of authentication technologies is best for you is a complex choice, and you have many options.
For example, you may decide to use AD Connect for only users in a specific AD domain or OU, while using Essentials Experience for others. You may decide to integrate user accounts, while managing shared mailboxes and distribution groups entirely as In Cloud accounts. You may also configure AD FS and SSO for one DNS domain while leaving available a set of backup user accounts that do not rely on AD FS.
