Ok Punta Cana & Puerto Rico are very nice vacation spots. It kind of depends on what you are looking for. Punta Cana has very nice beaches & inclusive resorts where you will be treated very good. DR is cheaper than PR as far as spending money & hotel prices. Airfare is probably cheaper to PR. But the downside is there isnt too much else to do. There are restaurants & clubs but thats about it. Anything else you want to see is too far & there really isnt much transportation, so you will basically stay in the resort. You need a passport & shots before you go. & do not drink the water. The resort food will be ok, but outside you need to be careful.
In Puerto Rico, you will probably stay in San Juan because thats the city. There is plenty of transportation to get you around. Even if you want to go to some sites outside of SJ you can take a tourbus. San Juan has nice beaches, but they arent as nice as Punta Cana's beaches. But you can go to PR's gorgeous beaches if you take a trip outside of San Juan. Vieques & Culebra Islands have gorgeous white sand beaches. San Juan also has tons of restaurants, clubs, casinos, shopping, historical sites like el Morro & more. The Bacardi Factory has a cool tour in nearby Catano. Also you can take a day trip to El Yunque rain forest & swim in waterfalls. Camuy Caves & Arecibo telescope are worth a trip too. PR is more safe to explore alone & the food & water is safe. Have fun whatever you pick
http://www.youtube.com/watch?v=CvOLT7fjQ3Q