There are a few lists traveling around on the internet claiming to be the Super Foods List. The first one I found listed collard, mustard and turnip greens as the highest in nutrients. Another one lists the Acai berry at the top.
I have spent the last few years concentrating on foods that help build stronger bones and muscles. I first started out with lots of berries: blue, black, raspberries, and cherries. I learned later that fruits cleanse the body and vegies repair tissue. I am now in the repairing phase as I don't crave as much fruit but do crave vegies. I didn't grow up eating much in the way of vegies except potatoes (smothered in gravy) and maybe green beans and such. And I wouldn't touch fruit. So this has been a big step for me to change over.
Now I crave greens if I don't have them for a few days. And I feel better after I eat them. I go by how my body feels and my intuition mostly, and when I do, I usually find out later that particular food was exactly what I needed.
So here is how I cook greens. You can get turnip greens, or spinach already frozen. Or fresh greens like collard, mustard and turnip and mix them. Put them in a pan with water enough to cover the greens. Or you can use chicken broth. Add some dulse and boil for about 20-30 minutes. Add butter and sea salt to taste and enjoy.
Greens are high in calcium and magnesium, vitamins K and A and manganese and folate. For you young people out there, I would recommend highly you eat these several times a week. Keep your bones strong!