From Robert Whitcomb's "Digital Diary,'' in GoLocal24.com:

Worcester’s bonds are rated Aa3 while Providence’s are a much lower Baa1. Worcester is in most ways a considerably less important city than Providence, and with a smaller economic and institutional base.

So what explains the rating difference? I’d guess Providence’s continuing failure to get its pension and other employee costs under control is the biggest factor.  That’s at least in part because Worcester has a city manager system,  which encourages professional (“technocratic’’) administration with far more insulation from political and special-interest pressures (e.g., municipal unions) than you get in a traditional mayoral system like Providence’s. The lower the bond rating, the higher the interest rate that a city must pay and the higher the taxes to pay the bond interest.