Common varieties of kale are Lacinato (Dinosaur/Cavolo Nero/Tuscan), Red Russian and the curly Redbor kale. They are certainly interchangeable–all working well in braises, soups, stews, stir fries, in pestos or raw, in salads or as chips. I do particularly like Lacinato kale for salads and in the beloved Tuscan bean and vegetable soup ribollita. Kale has rich culinary traditions all over Europe and Russia and South America. The famous Portuguese soup caldo verde is a favorite.
I almost always use the stems. Many recipes advise cutting them out but they tend to be quite tender and delicious and chopped finely are easily integrated into most any dish. Kale keeps for about a week in the fridge in a plastic bag. If it dries out you can revive it by soaking in cold water. When the leaves start yellowing it’s beginning to turn. Remove any of those leaves and use the rest post haste.
Kale is often touted for its nutritional benefits and it certainly has many, containing lots of calcium, betacarotene, vitamin K and C, and the anti-cancer chemical sulforaphane.