Most giggling could be replaced with several synonyms depending on the context. It could be replaced with "most amused," "most gleeful," "most jolly," "most lighthearted," "most playful," or "most joyful" among others. The word "giggling" implies a light and playful mood, so the synonyms should reflect that tone. If the context leans towards being more joyful, then "most joyful" might be more fitting. On the other hand, if the context leans more towards being playful, "most playful" could be more appropriate. Ultimately, the synonym chosen should capture the nuance of the situation accurately.