Ethereum classic is the best altcoins to invest for huge gain before 2018
 In 2017

    New Monetary Policy (ECIP-1017)
    Emerald Wallet
    Dapp SDK (based on Emerald Project)
    Standalone & embeddable EVM (with debugger for EVM code)

In 2018

    Light client for IoT and Mobile
    Scalability improvement and sharding (towards to 1,000+ tx/sec)
    Improve cryptography on EVM (for zero knowledge proof, homomorphic encryption, etc)