The truth is you can get the "best deal", "highest approval amount", and also "royally screwed" from any type of lending source - a mortgage broker, a mortgage banker, a bank that has a mortgage division, a credit union, etc. There isn't one "type" of loan originator that will always be better than another.
Explore at least 3 options, and preferably at least 1 mortgage broker, 1 mortgage loan officer who works for a bank, and also one that would work at a smaller direct mortgage lender (not a broker, and not a bank, just a mortgage lender who arranges loans and sells them afterwards - usually to the banks)... it wouldn't be a bad idea if you had the time to interview up to 6. That way you can get a feel for how each does business, because not every mortgage broker is the same as another mortgage broker, etc.
You'll want to ask what the pre-approval process entails and how long it takes. Will the underwriter who will be allowing your loan to close be the person reviewing your file as part of that process? Will it just be the loan officer reviewing your information? Will they even ask you for documentation?
You'll also want to ask what types of programs they offer, and once your documentation has been thoroughly examined you'd want to get what options would then apply to you, as well as ask what your loan officer thinks would be the best loan program for your situation.
You'll want to ask what type of fees & costs you could expect to incur along the way (credit report, earnest money deposit, home inspection, appraisal fee, closing costs, etc.), how much those costs are estimated to be, and when they are expected to be paid (at the time the service is performed, at closing, etc).
You'll also want to ask what type of loan terms can they offer you if you were to lock in your interest rate today.
You should also ask when & how they will be available - are you someone who likes to discuss things after the normal work hours on the phone? In person on a Saturday? Through email?
There are more variables to think of, some will be important to you and others will not, however I truly believe that you will have a feeling inside of you of pure comfort when you have found the loan officer who will be the perfect fit. You will leave the conversation having a full understanding of the road ahead and what is expected of you, as well as you'll feel the loan officer has left no stone unturned when going over your situation.