I think bitcoin is an asset,because the value of bitcoin keeps increasing.If you hold bitcoin for long time you can have more profit while you sell it.
I think bitcoin is both assets as well as currency. But more commonly we use bitcoin as currency, we can use bitcoin for shopping in most big shopping center, in fact they accept bitcoin as currency for shopping. therefore i will like to say that bitcoin is more as currency and in future it will even be use as fiat in local shops also depending on the increasing number of bitcoin users.