Bus by an octopuscard or airport express, which is cheaper?

Any suggestion regarding which one is the cheapest ride? A cab, bus buy an octopuscard or airport express? Our itinerary for day1 is HKIA to TST to NP360 to Victoria Peak to Madame Tussauds To TST again? For 2nd Day is TST to Ocean Park to Avenue of stars to TST? For day3 is TST to disney land to night market to TST? Day 4 is TST to HKIA? Thanks! Btw, i will b travelling with my mom and 3kids age below 11years old.. Thanks again!