Here is my oppinion.
First a knowlegable go get 'em loan officer is more important than the lender you choose. First of all all lenders go to the same place for the mortgage, second of all the biggest thing that influences what you will pay is the market movement.
In this market many lenders are taking 3 months or more to fund loans. I actually quit a job last June becuase the company I worked for started doing that. Here is the thing, you can only lock in the rate for so long, extensions cost money. So if they do not close the loan quickly you wont be getting the rate they quoted anyway...er if rates go up. They seem to want to deliver that rate anyway if rates go down.
When shopping for a loan be sure to ask, "when can I lock that rate in?"
First of all many lenders do not lock rates. Second of all many lenders are just using bait and switch tactics. If they won't lock your rate for several weeks you are really rolling the dice to go with that lender. Also they can quote you any rate they think will get you in the door rather than the true and correct rate. I really wish the regulators would crack down on this, but for now they are turning a blind eye to it.
One of the new things happening are these large boiler room lending operations, you know who many of them are because many of them advertise non-stop on the radio. Lending Tree, Cash Call and Greenlight come to mind. They have a alot of people answering the phones and they need to make the phones ring, so they more often than not they cut corners by advertising rates that you are not likely to get.
The major banks BofA, Chase etc. have figured out that they can charge more and they do. Right now the are also known for taking a long time closing loans.
I would then say your best bets are: smaller banks, credit unions, smaller mortgage bankers and believe it or not many mortgage brokers are a great choice. I feel lucky to work for a smaller bank that has great rates low fees and closes quickly.
Finally, when you do apply for a loan, the lender will be asking you for a lot of stuff. Give it to them as quick as possible otherwise it becomes your fault the loan did not close quickly.