Essential or Standard for AD?

Hi.

A friend at non-profit has a Server 2012 Essential AND a Server 2012 Standard.  Neither one has been setup with users/Active Directory.  He wants me to come in and setup users and configure one of the servers basically as a backup server.

Which one should I use for setting up user accounts/AD? 

I'm a self taught geek but I want to make sure I choose the right one.

Thank you.

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