The phrase "most hot-air" implies excessive talking, boasting or empty promises. Some antonyms or opposite words for this might include straightforward, truthful, trustworthy, honest, or candid. These are all adjectives that indicate a person who is genuine and sincere, and not prone to exaggeration or deception. Other antonyms for "most hot-air" would be concise, factual, objective, and realistic. These words describe someone who communicates in a clear way, without extra verbiage or attempts to impress or manipulate others. Ultimately, using these antonyms can help to convey a sense of integrity and authenticity, which can be valuable in personal and professional relationships.