"Settling upon" is a phrase that generally denotes finality - that a decision has been made or a choice has been selected. Its opposite, then, can be found in words or phrases that represent uncertainty, indecisiveness, or the potential for change. Some possible antonyms for "settling upon" might include: wavering, equivocating, hesitating, vacillating, deliberating, considering, weighing options, or exploring alternatives. Each of these words suggests a process or state of mind that is different from "settling" in that it is not yet finished or resolved, and that may be subject to change or revision.