When it comes to antonyms for "most good-hearted," there are several words that come to mind. One of the most obvious is "cold-hearted," which describes someone who lacks empathy and compassion for others. Another antonym is "selfish," which indicates that a person is primarily concerned with their own needs and desires, rather than those of others. "Malicious" is another word that is the opposite of "good-hearted," as it conveys a sense of ill-will and intent to harm. Finally, "cruel" is an antonym that suggests a lack of compassion and a willingness to cause pain or suffering to others.