Airport Express Travel Pass or Octopus card in Hongkong

There are 4 of us travelling to HK and wanted to know which is the best/ cheapest option to travel from the airport to central city. we will only be there for 2 days and will also be traveling to Ocean Park. Can you use the same card for that sector i.e bus 629 to Ocean park. we would also be considering going upto victoria Peak maybe via cable car ??

Any pearls of wisdom welcome