Generic answer to your question. The best agent is born from the advisor who takes his time to explain the process and listens and answers all of your questions. He educates you so that you could help your son to make a decision between pro ball and college. He gives you a copy of the player's union contract and goes over every section. He is there on the other end of the line whenever you call, not his secretary. He has never told you he is the best, but you know from his personal track record his clients like him as a person. He wins your trust and your confidence. He isn't a sleaze because he won't take any part of your son's bonus money, only the extra he negotiates after your son agrees to go pro. He is smart because he knows that being honest with you and your son will someday payoff when your son signs a contract worth more than $800 month. He also is smart not to get into public arguments that might make all other advisors/agents look bad.
IMHO that is who is the best agent.