I'd make them completely from scratch if you can. That way you know exactly what's in it. I use Whey protein powder (NOW Brand). 1 scoop powder, 1 cup coconut milk, 1 cup frozen pineapple, 1 T flax or chia seed, blend. Our son cannot have milk based products so I use egg white protein powder instead of the whey. He loves chocolate, so I make his with 1/2 scoop egg white protein powder, 1/2 cup frozen banana, 1 T flax or chia seed, 1 cup unsweetened almond milk.
I found that you have to experiment with different fruits and milks to get a taste that you will like. I recommend using frozen fruits though so that you will have a more thick smoothie.