A new report about the nation's rental markets shows a dichotomy between those where apartments now rent at a discount relative to their long-term trends and others where housing is so tight that renters are paying steep premiums.

Renters in at least 21 of the measured 100 metropolitan areas are enjoying discounted rates. Boise City, ID offers the best break, with the typical unit renting at a 5.45% discount. Other cities in this category are Austin (3.27% discount), Phoenix (3.15%), Las Vegas (2.88%), and Spokane (2.62%). According to the report, these cities experienced rapid population growth and multifamily developers responded by overbuilding.

As a result, "it's likely that renting is the better option than buying in these areas," said Ken H. Johnson, an economist at Florida Atlantic University and one of three individuals for whom the Waller, Weeks and Johnson Rental Index on which the analysis is based was named. The others are Shelton Weeks of Florida Gulf Coast University and Bennie Waller of the University of Alabama.