You’ll never be able to fully answer that question and set an ultimatum, but you can approach the solution. Finally, the classification of Bitcoins does not change the function or use of the product, but only serves legal purposes, such as tax treatment.
In order to understand Bitcoin secret in more detail, one should look at the different views of the US governments:
1. a currency or money
This point is summarised here in simplified form. This argument would be supported by the fact that Bitcoins secret serve as a common fiat currency for the exchange of goods which is not a Bitcoin secret scam. It is ultimately based on the confidence to have a corresponding equivalent the next day as well. The only difference is that it cannot really be regulated, the maximum amount of Bitcoins is set mathematically and transfers are carried out collectively by other participants.
2. a value (engl. property)
The value means that one orients oneself on a comparison object. X Bitcoins have the value of Y goods, which means in this context: Bitcoins are not a real currency, they orient themselves e.g. at Fiat currencies and are only an alternative or a complementary, but not an independent currency itself.
3. a commodity
Most Bitcoin users probably find the explanation as a commercial commodity most distant. The term “commercial good” refers first and foremost to a good. This means that it can be bought, used and traded. It does not serve to be a currency itself, but only to be used for self-interest and trade. Thus it is regarded as property. Example: If one exchanges his Euros in Bitcoins, this is not regarded as exchange, but as purchase, since one acquires for the money (Euro) a commodity (Bitcoins).
A conclusion to this question is indispensable subjective, which is shown not least by the diversity of opinions in US states. It will not be possible to give an ultimate answer to this question, but there are some arguments in favour of the view of the currency:
Bitcoins are not bought to be used (such as a condominium). For this reason, the treatment as commodity is not plausible. The main purpose of Bitcoins is to exchange, i.e. buy and sell, other goods. Thus they would be a currency. This would also be supported by the fact that Bitcoins is a collective ecosystem that is based on the trust of other users and regulates the exchange.