Since the vast majority of mortgages are resold they meet standard underwriting qualifications. Thus by extension the mortgage brokers simply markup mortgages that you can find cheaper elsewhere. The markup is typically seen in the junk fees associated with underwriting the mortgage or markup on the appraisal and so forth. Now why would you chose to pay more for something you can readily find via a Google search?
Having said that I would use one of the largest credit unions, not a local one. Many CUs are open to you if you make a small donation to one of the charitable organization that furthers their base membership. The largest in the world, Navy Federal, operates this way. Here is a list of the top 50
Top 50 Credit Unions In The US