Quick answer: private car, bus or train
Compare the whole Singapore-to-Muar journey, not only the long-distance leg. A private car can be quoted from one Singapore pickup point to a specific Muar address. Bus travel usually centres the plan on a terminal and timetable, while a rail journey may require current service checks, connections and onward transport. The practical choice depends on group size, luggage, mobility needs, budget and how many transfers the group can manage.
