I stay for 7 days in hongkong as tourist from austria what is the best octopus card?

Hey, you can buy an AE travel pass with either one or two AE single journey(s) plus 3 consecutive days of unlimited travel on MTR. After the unlimited 72 hour use on MTR, you can top it up to use it for another 4 days.

Or you can just buy a regular Octopus Card for transportation. Thus you can enjoy discounts on any modes of transportation.