Juicing extracts the liquid and most of the nutrients out of the fruit or vegetable, concentrating most of the nutrients, as well as the sugars, in the juice, and leaving behind all the fiber as pulp. If you've ever juiced a fruit or vegetable, you probably noticed that a seemingly small amount of juice gets extracted compared to the size of the fruit or vegetable that you started with. For this reason, if you extract enough juice to fill an 8- or 12-ounce glass, you will consume significantly more of the nutrients as well as sugar from the fruit and vegetables because it would likely be too much to eat all those same fruits and vegetables whole (notice how much pulp is left behind?). The main benefit of juicing is that there's no fiber to slow absorption, so the concentrated nutrients are very quickly and easily absorbed through your small intestine, straight into your blood stream. However, the same thing happens with the concentrated sugars, and juices cause sugar spikes. Fruits such as bananas and avocados (yes, technically avocados are a fruit) cannot be juiced, and fresh juices must be consumed immediately because without the fiber, the nutrients oxidize quickly upon exposure to air.
Blended smoothies make use of whole fruits and vegetables, and skins don’t always have to be peeled off if you’re using a high-power blender such as a Vitamix. So in addition to the liquid, nutrients, and sugar, you also get all the fiber plus any nutrients that stay with the solid parts of the fruits and vegetables, including the skin, which often contains the most nutrients. The nutrients are not concentrated because you are consuming the entire volume of the fruits and vegetables in the smoothie, including all the fiber. In fact, the main benefit of a blended smoothie is all the fiber, which fills you up, slows absorption of sugar, prevents sugar spikes, cleans your intestinal tract, and keeps you regular. The nutrients are absorbed more slowly from a blended smoothie than they are from fresh juice, and more of the nutrients are accessible for absorption after being pureed in the blender compared to chewing the whole fruits and vegetables in your mouth. Another benefit is that nuts and seeds can also be added to give the smoothie a creamier texture and richer taste. Bananas and avocados can also be added to blended smoothies. Plus, smoothies can be stored in an air-tight container in the refrigerator for several hours or even overnight if you don’t use bananas because nutrients in a blended smoothie remain intact with the fiber and don’t break down as quickly.
I personally prefer a green blended smoothie over green juice because I like getting all the fiber along with the nutrients, I like being able to add nuts, flax or chia seeds, bananas, and avocados, it fills me up, I don’t get a sugar spike, and I can save some for later.