It has properties of both. Tax authorities will eventually give their opinion on this. Through its properties of finite quantity, fungibility, and resistance to forgery/duplication, it acts as a commodity. It can be sent directly between any two parties anywhere on Earth, without regard for the quantity transacted or physical distance, to act as a currency.
By the way, establishing trust in a trust-free environment through cryptographic proof-of-work is a remarkable invention. Sending economic value, cheaply and securely, around the world in minutes, not days/weeks, is a remarkable invention. This is where the value comes from.