About topping up hong kong airport express travel pass

You said that the card will function as a normal octopus card, so does it means that i can't enjoy my 72 hours unlimited rides?
What would you suggest, since i will be in HK for 5 days and 4 nights.. Should i buy 1 octopus card and 1 AE travel pass? Or i just buy AE pas and top it up? Thank you