It's a good question. Some would say the safest bet is in Ethereum.
More risk but more potential reward: Stellar Lumen, Cardano, Eos, Bitshares. All have very strong teams of people and are very legitimate and likely to be at the top of the pile in coming years.

Verge, reddcoin, bytecoin....I don't know about those for long-term holds if you only have a little money to invest. Ride the wave but don't cling, no matter how many times you're told to HODL.