I believe that BTC is both an asset and a currency. Some people use it for their everyday payments as a currency and others to hold value (asset).
I also think when more merchants start to accept BTC or any other altcoin as a form of payment, people in general will be more comfortable to use it as currency and eventually BTC will replace fiat.
It is the manner at which people uses bitcoins which is determining on whether bitcoins is with an asset or a currency. But in my opinion I will consider it to be both and maybe more, since others are using it for other things as well.