The word \"big\" in the title could be confusing, especially because there are thousand different opinions, some people only called Bitcoin big cryptocurrency, some people think of first 5 or 10 cryptocurrencies when said big. Confusing could also be the point of view, what big really means, does it mean high price, or functionality that some digital currency is providing to its users or some other factor are included?
So it is very difficult to answer to the question what cryptocurrency is next Bitcoin. It could be Ethereum. Ethereum is very good platform, based on smart contracts, it is used in most ICOs (initial coin offering). Another cryptocurrency that is based on smart contracts is Cardano, and people thing that Cardano might be able to reach Bitcoin level. Bitcoin is now crypto star, everyone is talking about it, so if we are going to find the Bitcoin rival, we must focus on other altcoins, not only Bitcoin.
Let\'s go back to our next \"big\" cryptocurrency. If you use the term big for the top 5, then next big cryptocurrency should be somewhere in the top 10-15 for example Cardano, Tron and Stellar. If you use the term big for the top 10 than the next Bitcoin is somewhere in the top 20. Monero and EOS are potential candidates.
To make a resume here, it is very hard to predict future, especially when it comes to the cryptocurrencies, its market is very volatile and it is almost impossible to predict which cryptocurrency are going to explode next. The best advice is to spend few hours daily researching about cryptocurrencies, what functionality they are providing to its users and adoption rate of the cryptocurrency and so on.