The antonyms for the word "most smiling" would be "least smiling" or "unsmiling". When someone is referred to as the "most smiling" person in a group, it indicates that they are cheerful, warm, and friendly. However, the opposite of this term would be someone who rarely or never smiles, giving an impression of being cold or distant. Someone who is described as "unsmiling" may be perceived as unapproachable or unfriendly. While being the "most smiling" person has its advantages, being "least smiling" can also have its benefits, such as being taken more seriously in a professional setting.