It doesn't matter if you use a realtor or broker, or broker associate. While there are technical differences, the differences are transparent to you the buyer, and the service to the consumer is the same.
First, talk to a preferred lender and address your questions regarding loan eligibility. Once you know you qualify for a mortgage with terms you find agreeable, then choose a Realtor of your liking. You can search for one in your local area using Trulia and even read up on candidate recommendations.