You can use regular M&M's for baking. I've tried traditional and peanut M&M's and they both work fine. Baking M&M's are a little bit easier to eat but the regular-sized M&M's are so pretty in cookies. I like to save some M&M's separate from the batter to add to the top of my cookie dough balls before baking. This way I can ensure that all the cookies get some M&M's on the top for color!