One big site or many little sites..which is better?

I'm working with a mortgage broker and they have a few different customer niches that they work with. For instance, they target newlyweds as first time homebuyers, people who are credit challenged, real estate agents, and people who are interested in refinancing, etc.

He wants me to revamp his website but had a question.

Is it better to make one huge site that targets all those different types of customers. Or is it better to make smaller individual sites for each type of customer that links back to the main site?

For instance...

1. Make a "Mortgages for Newlyweds" website that talks all about newly wedded couples type stuff and buying their first home and the things they have to do.

2. Make a "Morgages for the Credit Challenged" website that talks about how to fix your credit, what their options are, different low credit score programs, etc.

3. And a few more sites like the ones above.

Then, have a link on all of those separate sites that go to the main broker site that talks about their company, what they do, and even have them fill out a credit app. This main site can also have links to all of the separate sites.

So I guess the question is, from an SEO standpoint, is it better to have those separate sites provide backlinks to the main site? Or is it better to just make one huge site (their main one) that's loaded with all that individual content?