Upvote:4
HKD is pegged to USD. It's usually at a rate of HKD7.75 = USD1. It has been pegged for several decades now.
So technically there shouldn't be a difference with regards to purchasing using USD or HKD. If there is, the difference is marginal (less than 0.01%). You will find more fluctuation between JPY and HKD (and USD) because JPY is not "permanently" pegged to HKD or USD.
With that said, USD is generally more accepted than HKD, and you may find that the currency exchange you're changing money with will not accept HKD. As such, as a rule of thumb it is better to carry USD over HKD. Hope this helps.