I haven't been to Turks & Caicos so I can't compare the two but Punta Cana is amazing. The resorts tend to be spread out there so you definitely feel like you are 'getting away'. The sand is beautiful and the water is warm but Punta Cana is on the Atlantic so you can get a pretty serious surf which we loved but it's not your typical calm Carribean water. The weather was perfect all week.
We stayed at The Excellence which is our favorite all-inclusive resort down there with tons of restaurants, great rooms and an amazing & attentive staff. It's a little bit of ride from the airport but it's totally worth it.
I don't think you can go wrong with either location but I can highly recommend Punta Cana. We would go back there in a heartbeat. almost 7 years ago