What makes a good muffin ? Ivan

Today most cooking projects start off by consulting the Internet for recipes. A quick search for “chocolate chip muffins” returns a multitude of different recipes, and typically, we would look though the top rated ones and try to decide which one “looks best”. We would go down the ingredients list, make a few substitutions, depending on what’s left in the fridge, and maybe scale down the recipe, since we don’t have a whole dinner party to feed... But is it really OK to substitute sour cream for yogurt? What if I’d like to use soy milk instead of whole milk? And how do you split three eggs in half?