Your credit will have a big impact on what great deals you can get. Banks can offer great deals to buyers with excellent credit. If your credit is not perfect, then it might be better to go with a mortgage broker that will be able to find a great deal. However, you are free to shop around and compare.
After obtaining a pre-approval and confirming your qualified for the mortgage, you can have several firms compete for your business and obtain written quotes of their fees and other charges which will impact the APR on your loan.