There is no comparison.
nicer as a whole - Cabarete
More restaurants - Cabarete
Beaches - Cabarete beach looks nice but here Juan Dolio wins. But, many of the beaches are in front of apartment blocks and there are no loungers and you are not allowed to take food or drink or an umbrella. In old Juan Dolio you can sit on loungers in front of bars/ restaurants as long as you consume there or rent there. No option but a towel on the sand in Villas del Mar.
Juan Dolio is on the caribbean sea. Not far from the capital so lots of sightseeing there. Over the last 5 years it has slowly died as most hotels have been demolished to make way for apartment buildings, mostly owned by dominicans from the capital. In the week it is a ghost town. Nobody in the street. At weekends it is busy. As there are no tourists many businesses and restaurants have closed. There are a few left, mostly italian. The population is 85% Haitian and there is an informal curfew at night when any dominicans or haitians on the street are arrested. Many ex pats have left.
I have only visited Cabarete a few times but the beach seems fine, it has life, many good restaurants and supermarkets (in Juan Dolio you would have to go to nearby town of San Pedro), and would suggest it would be much better.
Matilda