Cooking with your dehydrated peppers is easy as well. If you're making sauce or chili, simply add them as is to the pot (if you are using slices, crush them first). They will rehydrate during the cooking process. If you'd like to use them on pizza or in salads, soak in lukewarm water for 20 minutes before adding them to your recipe.
Personally, I prefer slices, as it's more time efficient, and can be easily crushed before use. If you are dehydrating for pizza topping or in pasta salads, I'd recommend dices for presentation.