Take West Rail line and Tsuen Wan line Octopus fee:$21.9(Adult)/$11(for child/elderly and student)
$26.5(for Adult and student)$13(for child /elderly)(single ride tickets)
Take KMB bus No.968 fee:$21.4(for Adult and student)
$10.7(for child age under 12 or below and elderly)
So if you are student,you should take West Rail line because the fee is less than take bus.
But if you forget to bring the student Octopus,you should choose to take bus
Hope above information canhelp you!