Fruits and vegetables are like Ernie & Bert on Sesame Street: always grouped together but very different from each other. If you don't know Bert & Ernie, you should.
And you should eat more vegetables than fruits, by the way.
Both fruits and vegetables provide a broad spectrum of nutrients. The basic difference is that fruits are sugary and vegetables are not.
The good news is that the fiber in a whole fruit slows down the sugar absorption so it won't hit your bloodstream like a candy bar. The bad news is that too much sugar is too much, even if it's from fruit.
When we eat sugar, whether it's the white refined stuff, an organic apple, or a piece of whole grain bread (yes, grain melts into sugar), the pancreas secretes insulin. The job of insulin is to balance blood sugar, which is good because high blood sugar feels bad (fatigue, blurred vision, extreme thirst) and low blood sugar feels bad (dizziness, shakiness, sweating, headache, etc.).
When you eat more sugar than you need for immediate use (sitting at your desk eating chocolate, for example), insulin sends the sugar you don't need to the liver to convert to fat. Thus, it has been named the "fat-storing" hormone.
Generally, eating less sugar and foods that melt into sugar (fruits, pasta, bread, crackers, etc.) means lowered blood sugar and less body fat.
It's not the whole story, but it's a good rule of thumb.
So now back to fruit.
Berries are best because they are high in fiber (which puts the brakes on the release of sugar) and full of antioxidants. Tropical fruits like bananas, mango and pineapple add a lot of sweetness and flavor to a smoothie but a lot of sugar as well, so watch out.
My general suggestion is to consider 1/2 cup of berries 1/2 cup of chopped fruit like pineapple or mango, or 1/2 whole banana as 1 serving of fruit. for most of us, it's good practice to limit fruit to 1-2 servings per day.
A good rule for the other thumb: too much of a good thing can be bad.
Starting the day with a fruit smoothie or a stack of pancakes can be almost the same thing.
You've set yourself up for sugar cravings for the rest of the day. A serving of fruit with some protein and fat can be a good way to fuel your day. But if you are struggling with your weight or mood, you may want to try saving your fruit for the afternoon and stick to plants & proteins before noon. An omelette with greens and salmon or leftovers from last night's dinner is a great breakfast.
Staying off the sugar roller coaster in this way helps you stay mentally alert and undistracted by sugar cravings.
fruits are fine to eat for fun
eat plenty of plants for peak performance.
NOTE: Strawberries and apples are consistently on the Dirty Dozen list so eat these only when they are organically grown.