The main different between bitcon and the rest of the digital currencies, even eGold which was backed by something real (gold), is that it is decentralized.

That means that nobody "owns" the bitcoin network, so there is no central point of failure.

Previously, when a digital currency would get to the point of near critical mass, a government would step in and shut it down.

That, combined with the public ledger system of bitcoin, make it superior to any other cryptocurrency that has been attempted in the past.

It also does not mean that it will be the best, there's another cryptocurrency called Ripple which is both a currency exchange protocol and a currency (XRP) that is also gaining traction.