Non organic fresh would be the next best followed by canned. Canned foods retain a high level of nutrition as long as you use the juices they're packed in. The one drawback seems to be that they are higher in sodium.

    Preparation – Lightly steamed is the ideal. Raw is not necessarily healthier. Many nutrients are locked within the starch matrix of vegetables and fruits.These are unavailable if eaten raw, as raw starches are difficult to digest. Cooking breaks down the starch, releasing the nutrients. Foods are also safer when cooked, killing bacteria, parasites and other microorganisms. Some vegetable eating animals have three or four stomachs and regurgitate several times. Imagine how difficult it is for people who have weak digestion to absorb nutrition from raw foods. On the other hand, raw foods contain enzymes which aid in the digestive process. These are very sensitive to heat and do not survive baking, broiling, etc. Steaming brings the best of both worlds breaking down the starches and saving most of the enzymes.

     A light stir fry, less than 10 minutes would be next. I like to throw veggies directly on the grill at low heat. The cooking methods requiring high heat for longer lengths of time not only kill the enzymes but begin to break down the vitamins and fatty acids.

     Super heating food also produces the carcinogen acrylamide. Acrylamide cannot be created by boiling, and very few uncooked foods contain any detectable amounts. Browning during baking, frying or deepfrying will produce acrylamide and over-cooking of foods will produce large amounts. Acrylamides can also be created during microwaving.

         Lastly, if you boil your vegetables, you'll want to use the water they were cooked in since that's where most of the water soluble vitamins (all of the B's plus C) will end up.