The word "un-sightlier" implies something that is unpleasant or not visually appealing. Antonyms for this word could include words such as beautiful, gorgeous, and stunning. These words suggest something that is aesthetically pleasing or attractive to the eye. Other antonyms could include the words attractive, lovely, and pretty, which suggest a certain level of charm or elegance. Using these antonyms in place of "un-sightlier" can help to convey a more positive tone and create a more desirable image, whether describing a person or an object.