The healthiest food for your kitten depends on their specific needs and preferences. In general, a commercially produced food is less likely to have risky or untested ingredients. Bigger brands and companies typically complete a variety of tests to help ensure their food is safe to consume and meets nutritional standards.
Look for kitten food that meets Association of American Food Control Officials (AAFCO) safety standards (their quality seal or statement will be on the back of the bag). This nonprofit sets nutritional standards for pet food in the United States.