It depends on you. all altcoins are well purchased if the coin has a large decline. all depends on how you choose and rate for your investment.As the Blockchain technology evolved, we have countless options in the cryptocurrency list to invest.

The top cryptocurrencies to invest might not be very popular or common to all the traders. Different people will invest in different cryptocurrency.

Before thinking of investing any cryptocurrency, it is important to understand their features and potential in the long turn. In my opinion, the best cryptocurrencies to invest in 2019 other than Bitcoin and Ethereum are Zcash, Dash, Neo, Cardano, Tron etc
The best altcoins are those who aren't dead and won't be dead as the days goes by. They are potential enough to survive the unstable market and whatever the possible struggles to come. You can do search of them.