Largest ones are Bitcoin and ETH. There are some other altcoins, but who can predict price movements, even in some months ahead. So if you invest in BTC or ETH, you can hope, that after three years, the price will go up. 
I think you have to diversify your capital so that it will be safer and more profitable, you can choose bitcoin and Ethereum for long-term investments and other altcoins for trading, why buy this year? because this year prices have dropped very deep and it's a good opportunity to sell