no doubt about BTC, it's always the best  altcoin with the highest value of all. i think next is etherium, LTC and ripple.

I suggest you buy and hold NEO and Monero. These are very promising altcoin. NEO is called the Asian dragon, it was born in China, NEO has the technology and direction is quite similar to Ethereum. I believe in the future NEO will grow and compete with Ethereum. Monero offers privacy, every transaction with Monero is completely anonymous. No third party can find the Monero user information.