While rate is important, you have to consider the overall cost of your loan. Pay close attention to the APR, loan fees, discount and origination points. Some lenders include discount and origination points in their quoted points. Other lenders may only quote discount points, when in fact there is an additional origination point (or fraction of a point).
This difference in the way points are sometime quoted is important to you. One lender will quote all points, while another lender may disclose an extra point, or fraction thereof, at a later time--an unwelcome surprise.
Within 3 working days after receipt of your completed loan application, your mortgage company is required to provide you with a written good-faith estimate of closing costs. You may want to consider requesting a GFE from a few lenders before submitting your application. With a few GFEs to compare, you can get a feel for which lenders are more thorough, and you can educate yourself regarding the costs associated with your transaction. The GFE with the highest costs may not indicate that a particular lender is more expensive than another--in fact, they may simply be more diligent in itemizing all fees.
The cost of the mortgage, however, shouldn't be your only criteria. You should feel comfortable that the loan officer you are dealing with is committed to your best interests and will deliver what they promise.