A lot of alts are very good. But you need to make your own research work before investing in. The most promising altcoin, as for me, it`s ETH which provided smart-contracts, ERC-20 and also develops as well. Some good coins for your check: EOS, NPXS, ADA, TRX.
I generally agree with this, but I will add that it is worth considering not only ERC-20, but also currencies with the DAG algorithm. I think these coins in the future can give excellent growth.