When picking a mortgage lender you are looking for experience and responsiveness. Most lenders have very similar loan programs and rates. However, an inexperienced loan officer or sloppy loan processing can cost you hundreds of dollars in fees and thousands of dollars over the life of your mortgage.
Make sure a mortgage lender that asks a lot of questions, seems sincerely interested in what you are trying to achieve and is responsive to all of your questions and requests. During the loan process, which typically takes less than 30 days, you should be in almost daily contact with your loan officer and processor (the person managing the documentation and qualification process).