My wife recently worked with a mortgage company to get an idea of what type of mortgage we could be approved for. In the spreadsheet they sent, they did a pretty good idea of itemizing the costs. My question is - when 'shopping' for a mortgage, what do the companies compete on? Is it closing fees, mortgage rates, etc.? How much difference could one company potentially vary from another? What's the best way to compare one company to another - do we need to go through the pre-approval process for each company we want a rate from? We're trying to decide how much effort should be put towards shopping around for a potentially better deal.