With the rise of the salad restaurant (think Tender Greens, Sweet Green, Chop't), the kale craze, and the vegan revolution – it’s a good time to examine the building blocks for the oldest healthy dish in the books. With a wide variety of salad greens available, it can be hard to differentiate among them– which is the healthiest? Which has the most vitamins? Which is lowest in calories? And which tastes best?