"more appropriate" is highly subjective. Which has higher value to your organization? If you create a workflow to do this, you'll be slightly less dependent on the external company, but you'll have to take the time to do it yourself when you could be doing something else potentially more valuable, and now your business rules for creating Customers are disjointed (some in Script, some in Workflow). If you hire it out, you keep all your Customer business rules in one spot, but you have to pay, and you don't reduce your dependence.