Massachusetts is more expensive but generally better run - better schools, more business friendly, stronger tax base, etc. Real estate taxes are significantly lower but properties are generally assessed higher (eg Cumberland is $15/thousand vs bordering towns in MA - north Attleboro is $12.79, Attleboro is $13.69, Wrentham is $12.62) Sales tax is also slightly lower. Lowest tax rates in RI are in towns where significant portion of residents are out-of-staters who aren't a drain on services (Newport, Narragansett, Charlestown, Westerly, little compton). Most other towns carry the financial albatross otherwise known as the city of Providence around their necks and tax the absolute shit out of your property. Rhode Island is definitely cheaper cost of living but outside of East greenwich and Barrington the public schools are really not great.

All that being said, I moved here a decade ago from Massachusetts and have no plans to move back. As frustrating, corrupt, and annoying as RI can be, it is a beautiful state, especially South county. It is very different in a way that's hard to explain. it was settled differently than Massachusetts, where towns were set up in a very cookie cutter way around a central common, so many towns are really very different and distinct villages with different vibes that someone just drew lines around (saylesville, valley falls, and central falls would really make more sense as one town, but they're split between three.) Again with Cumberland as the example - valley falls is very working class mill village, Arnold mills is very 50s Americana, Cumberland hill is very white collar wealthy, West Wrentham is woodsy with lots of space and large forested lots. You can apply this to most towns in RI. Traffic in Massachusetts is additionally absolutely infuriating - as annoying as the 6-10 cluster fuck can be, traffic on 128 starts at 530 in the morning and spreads down to north Attleboro by 700 - like "why the fuck would anybody live here" type of traffic. am also of the opinion that Rhode Island beaches are much better than MA beaches by and large with warmer water and less seaweed(and no Cape traffic, which makes rt 4/rt1 in summer look like a cakewalk).