Altcoins that could provide solid development, innovation, and most of all, usability will most likely succeed over the long term. There are many prominent altcoins in the market, which you could buy right now with their own use cases. If you've been paying close attention to their price movements, they have been rising in value exponentially during the year, reducing Bitcoin's total market dominance.

Thus, if everything continues as is, altcoins would be widely used in the mainstream world for various applications, while Bitcoin will remain as a store of value.

The altcoins which prove to have better stability, technology, and usability, would likely remain on top and overcome other cryptocurrrencies on the markets. There is a fierce competition on which provides faster transactions, anonymity and user acceptance from around the world. Just my opinion.