HKD would be an interesting one as China is building up gold reserves and surely HKD will gain when China stops fixing to dollars. But you are trusting their government to do anything but favour themselves.
Their holdings of trillions in US debt will cause them problems and its most likely the currency suffers for that
The Euro is where I'd keep it in Fiat.
No their interests are with politics not keeping currency worth. They would devalue and make currency holders pay to service centralised debt. If you want to go Euro then hold Swiss francs as you can at least hope one day that country releases the tether they hold over Euro before it goes over a cliff and so your losses are limited. Swiss hold about 10% of worth in gold backing and they were the last gold backed national currency to operate up until 2000
The one I'd choose if I had large amounts (spare) in a currency I had no debts in, it would be Australian dollars. Its a large country with many resources, not that many people and they have an interest in maintaining a link to commodity industry. They are more aligned to Asia and actual production not so much politics and old western dominance now based on consumerism. Also its a national bank which operates a national mint and even their own gold mine, they are far more likely to link or respect gold exchange long term when its a part of the countries national production already.
Especially if that industry rose as dollar fell, its likely to benefit even fiat investors in that country
