For fruit, fresh is my first choice, but I often do use frozen fruit, especially berries. Nutritiously frozen fruits and vegetables, even canned can be a good choice. Sometimes they're actually a better choice than fresh (if the fresh isn't so fresh, if you know what I mean).
Because they're canned or frozen at their peak, they can be better than "fresh" produce that has sat on the shelf, or in some warehouse for months.
I use frozen berries to make smoothies and slushies. I just blend (still frozen) in a blender with milk, juice, water, Crystal light, or diet citrus soda.
Apples and oranges are often very good in the fall and winter. Good pineapple is often available all year round, especially if you pick the super sweet hybrids (usually "Gold" is in the name, like Dole Gold).