These days, salads made with lacinato kale or rainbow chard are inferred to be much healthier. In some ways that is true, since kale - a cruciferous vegetable - contains phytonutrients not found in other plants. Chard, with its bright reds and yellows, offer anthocyanins and other antioxidants which are much less prevalent in green-colored veggies.
Is green leaf lettuce good for you? It may be plain Jane vanilla in the eyes of many, but it deserves respect. Why? Because when you compare the antioxidant value of green leaf lettuce vs. kale. vs. spinach, the findings may surprise you. Raw green kale comes in at 1,770 while raw spinach is 1,503. Now compare those ORAC values versus green lettuce which is 1,532. They're all fairly close, right?
And perhaps the most underappreciated for being healthy and nutritious is the red variety. If you look at red leaf vs. green leaf lettuce nutrition, you will discover that their vitamin A, vitamin C, calcium, and iron content is almost identical. But it's their antioxidant content which is quite different - red leaf tests out to be 58% higher than green leaf, 37% higher than kale, and 44% higher than spinach.
That of course brings about the logical question, why aren't restaurants and food providers peddling red leaf as a superfood? Partly this is because of consumer demand (consumers generally consider kale healthiest) and probably, some self-interests are involved, because leaf lettuce perishes quickly and therefore isn't ideal for restaurants to keep on hand, while kale has a very long shelf life - making it ideal for food services and those premade salads you buy at places like Trader Joe's.
USDA Database for the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 - Prepared by Nutrient Data Laboratory, Beltsville Human Nutrition Research Center (BHNRC), Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA) - May 2010