I believe both Fiat and Bitcoin serve different purposes and follow different rules, which makes it hard to say one is better than the other.

While Fiat has been depreciating, Bitcoin on the other keeps appreciating in value since inception, however, the lack of popularity (and sometimes associating it with Ponzi schemes) and government's interference makes it difficult for people who do not understand what Bitcoin( cryptocurrency) is about to not readily use it. This is one of the major reasons while Fiat still has an upper hand, despite its depreciating value, over bitcoin.