We've rounded up the 5 vegetables highest in different key nutrients. That's helpful if you're trying to load up on, say, fiber or potassium. But the bottom line? All veggies are good veggies. The rankings are based on equal weights of vegetables. A typical "serving" of vegetables is 3 oz. That's roughly 1/2 to 3/4 cup of cooked vegetables, or 1 1/2 to 2 cups of raw leafy greens. (But hey, with only 15 to 25 calories in a serving of many veggies, why stop at just one?)