I like to use Database Roles and only grant permissions to the Roles even if the Role will only have one member initially. Consider that if a person leaves an organization you may delete their Login and Database User but the Role will still be there with the permissions granted to it and the person's replacement can easily be added to that Role and have the same permissions their predecessor had. That is just one benefit of using Roles, there are numerous and there really is no reason not to use them and avoid granting permissions directly to a User.