Antonyms for the word "most preoccupying" include "least concerning," "least engrossing," and "least distracting." These terms indicate a lack of attention or focus on the subject in question. Other antonyms might include "unimportant," "minor," or "inconsequential," which imply that the issue is not worth worrying about. Alternatively, antonyms could reflect a sense of relaxation or calm, such as "peaceful," "restful," or "serene." In any case, these words suggest a state of mind that is diametrically opposed to one that is strongly preoccupied, concerned, or focused on a particular matter.