While municipals generally carry lower yields due to their tax benefits, beware that they are more risky than comparable Treasury securities. Municipals can default since, unlike the federal government, they do not have the ability to print money. The most recent (and largest ever) city to declare bankruptcy is Stockton, CA. See the article here, Fox News.
Dolvin, Steven D., "Municipal Bond Risk" (2012). All Chapters. 22.