I've read that heat can reduce the vitamin, but not mineral, content of food. Prunes are supposed to be loaded with antioxidants. When I want them stewlike, I boil some water, then pour it over them in a glass container and let them rehydrate overnight. Sometimes I flavor with lemon; other times with spices - cinnamon, cloves, ginger.
I buy a brand of California prunes online that are not too dry and moist enough to eat without rehydrating, but not moist to the point of being overly sticky.
I was also buying organic prunes for a while and they were pricey. I couldn't find any information about organic prunes being better than nonorganic so I switched.

I found a big difference in the quality of prunes at Costco (Canada) compared to other grocery stores where I first bought them. The Costco prunes were far more moist and sweet-- delicious!