First, your Agent can do everything a Surrogate can do and much more. Second, with an Agent you reduce the risk that your wishes will not be carried out because the Agent will be following your written directions. Third, you may prefer someone other than the Surrogate to make these important decisions for you. Fourth, you could end up with several children or several brothers and sisters as Surrogates who may disagree. You can reduce the risk of disagreements between them or court challenges by naming your own Agent.
Some information is available in both English and Spanish.