The phrase "most down-at-the-heel" typically means very poor or dilapidated, and its antonyms can vary depending on the context. In terms of physical appearance, words like extravagant, opulent, luxurious or affluent can all serve as antonyms. Similarly, in terms of finances or social status, strong antonyms can include rich, wealthy, prosperous, privileged, or even successful. On the other hand, if the phrase is being used to describe a person's mood or emotional state, then antonyms could include happy, content, joyful, elated, or even buoyant. Ultimately, the most suitable antonyms for the phrase would depend on the specific circumstances in which it was used.