I think the classic big coins btc, eth, xrp, ltc all have a very promising future and can't go wrong with them. Altcoin is actually shaped like a currency in the real world, that every time the value of selling can be changed. in my opinion the coin will continue to rise is the volume and demad continues to rise, i think the ETH can rival the BTC because it cost more unstable compared to other coins.
Eth, Btc and Ltc are good ones. But there are more promising coins and blockchains. Waves and Nem are examples of this. Waves can do better things in the market. Nem is also a great blockchain project with mozaic technology.