Litecoin and here is why...

Ethereum is great but there are two things that give something value: utility and scarcity. Ethereum does not have a maximum supply and the utility that Ethereum garners is from smart contracts but there is a lot of competition concerning smart contracts, you have Neo, Stellar, Waves, Stratis and of course EOS. The arguement could be raised that Ethereum could have private smart contracts but the implementation of zero knowledge proofs or other privacy protocols will cost a fortune in fees.

Just like Ethereum, Ripple is great too but the issue with it is centralization. Blockchain is supposed to be decentralized yet the majority of coins are in the hands of a single company.

Litecoin is the best due to the scarcity of coins, I believe 84 million max. And Charlie Lee really is striving to make Litecoin one of the most valuable cryptos simply through usability/utility. Litepay is rolling out which will allow for widespread adoption of the crypto and they the "big" surprise for 2018.