Judgments are far more effective. Once the judgment is entered you have the enforcement apparatus of the state (Sheriffs/Marshals) to collect it through bank, wage and property executions.

Collection agencies can do little more than make annoying telephone calls
and write threatening letters. The hard core delinquent client usually ignores them because it knows that until it is served with a summons or receives an attorney's demand letter it has nothing to worry about. . The collection agencies have no ability to enforce anything. If they fail, the matter is usually referred to an attorney for court action. Save yourself the frustration and time. Go directly to a suit.

If the delinquent client has no assets to pay you, then neither the judgment nor the collection agency is going to work.