Each crypto coin is different, for its own reasons. That said, the short term value has been driven by speculation of investors, while the long term value will be driven by social utility, developer's apps, and real world application use for users, corporations, and nation-states.
On the long-term basis, the prices depend on the reliability of the currency, its investment and growth potentials. Bitcoin, Ethereum and Litecoin are the frontrunners in this regard. Since Bitcoin remains the most popular and well-tested cryptocurrency, its price will continue to grow in the future. The same applies to Ethereum price. It’s potential of growth is attracting more investments, which adds extra value to the price. Also, there is no novelty in the fact that the amount of bitcoins available for mining is slowly decreasing. This also results in the rise of Bitcoin’s price.