Some pretty good answers here.
I've done both and for our family the DDP didn't work. When we used them at TS we got too much food. I'm the only one who normally order's an appetizer and we never order desserts. However, since we normally have 2 TS's a day and go to signature restaurants we end up paying many TS's OOP because they weren't worth using the credits. Like Sci-Fi for lunch or the BD Fantasmic! package.
We also rarely use CS, the water parks being the obvious exception to that rule. We ended up using them for breakfast which isn't a good bargain.
The DDP didn't fit our vacation dining and I didn't want to change our plans to fit the DDP. With WDW being such a busy vacation I didn't like having to pay attention to the DDP.
Since both the credits and our OOP charges were both going on the KTTW we had to pay strict attention to the bill. Yes, there were some mistakes, but were usually easily corrected. The one big problem we had, was a cart's register wasn't working and on the way out the last afternoon 3 Mickey Heads were charged OOP instead of using credits but the mistake was caught after checkout and my BIL spent hours on the cell phone at the airport trying to get it corrected. He got the run around and eventually got so frustrated and had now used so many minutes that he just had to eat it so to speak. It was never corrected.