how long ago was it when you bought last? Some states have "first time homebuyer" programs, which can be used if you havent purchased a home in 7 or 10 years and make under some income. If you fit, the deals are good, and the programs are well-structured.
One key thing is to have an agent that you trust. Then the agent may give their trusted lender, who may or may not give kickbacks, and who ought to historically be pretty good.
If youre only looking for a verification of what you should be able to borrow, anyone should be OK... sometimes it might be worth looking at who the seller is using for their mortgage, if theyre just moving local. Sometimes there is a benefit to working that together - that is what I did when I bought my home, and it went really smooth, and was very low cost.
Mortgage brokers ought to be hurting bigtime at this point. Besides the poor state of the industry, mortgage rates arent particularly low compared to the federal funds rate (havent checked the Libor rate, which mortgages tend to be based, but IIRC it has dropped too), due to the level of risk that is acceptable at this point in time. As a result, Id guess that you have a lot of chances to "interview" lenders and get a good feel.
Perhaps others have used an online service... at the end of the day, the reputable company with the lowest cost is the best one, I suppose... and a decent credit union is always a good choice.
Remember... fixed rate and 15 years only! Pay it biweekly, with it going towards P&I biweekly (not sitting idle).
JMH