Here is my personal standard that I make - it is full of greens. This ends up being about 75% of the green smoothies that I make.

In a Vita-Mix 64oz/2l container:

2 Ripe Bananas
1/4 cup Goji Berries
1/2 cup Soaked Chia Seed
1oz Aloe Vera Juice (or fresh leaf)
1 cup Pineapple
1 T Super Greens (spirulina, chlorella)
fresh mixed greens: Kale, Chard, Spinach, Collard (this ends up being about 2 bunches of greens)
24oz Water

Blend till smooth.

Sometimes, when I'm in a sweet mood, I'll put in 2 or 3 fresh dates, or in a cold mood I'll use frozen bananas

Wow that's a lot of greens 

I don't think I could do that much - isn't it bitter?

That's a common question and the simple answer is no.

If you're new to green smoothies, it could be too much greens; I always suggest less greens (see green smoothie basic) and add more greens as you crave more.

It's definitely more flavorful but it's not bitter; the fruit, especially the banana creates a wonderful balance. We've been conditioned to believe that "good" taste is sweet and rich with fat. I really love green smoothies, they are incredibly flavorful and extremely complex.. they remind me of fine wines. 

Here are some examples of fruits that really cut the bitterness of greens:
Bananas
pineapple
cranberries
apples
lemons
blueberries
raspberries
kiwi

That being said, I have definitely made green smoothies that were too bitter for me even with lots of fruits. Sometimes I'll get a green that is just really pungent. Maybe it wasn't picked soon enough. Collards seem to get like that to me. Dandelions can also be hit and miss. My hubby loves arugula and the like in his smoothies and so does our son.  I just can't drink it. I don't like mustard greens either. Carrot tops are also inconsistent. Sometimes they are perfect and other times I just can't do it!

My sweetie is right, though, that our tastebuds definitely change the longer we drink our green smoothies. It's a fact, not just an opinion. I think I will always have a sweeter tooth than him, because that's just the way we are, but even my buds have changed and some things can actually taste too sweet for me. Now, if you know me you KNOW this is saying a lot!!

Oh, one other thing, once we started using a high-speed blender like the VitaMix, the flavor and texture of the smoothie were so much better. It was more homogenous, smoother, and creamier.

Have fun,
Shawna