Second-best city: Chicago 
Difference between rent and mortgage: 226.4%

America's "Second City" places second on Realtor.com's list because of high average asking rents ($1,630), low median mortgage bills ($720) and its many universities.

Several large schools call Chicago home, including Northwestern University (20,000 enrollees), the University of Chicago (12,300 students) and the Illinois Institute of Technology (7,800 pupils).

DuBois adds that 9.8 million-population Chicago is also America's third-largest metro area, "so you've got a large pool of potential renters."

That said, Chicago home prices have yet to bottom out.

Median asking prices on Realtor.com fell 3% over the 12 months ended July 31 to hit $194,000.

DuBois attributes some of the decline to the fact the Illinois requires banks to go through a lengthy judicial process to foreclose on homes. As a result, it's taking a long time to clear the state's backlog of distressed properties, she says.

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