Okay if you are consue with BTC and ETH let me introduce it to you.

BITCOIN (BTC)
- Bitcoin was invented by an unknown person or group of people using the name Satoshi Nakamoto and released as open-source software in 2009. Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services.

ETHEREUM (ETH)
- Ethereum is an open-source, public, blockchain-based distributed computing platform and operating system featuring smart contract (scripting) functionality. ... Ether can be transferred between accounts and used to compensate participant mining nodes for computations performed.

Now which one is best to invest/hodl for long term?
- Both are best to invest/hodl because if you do not have the 2 you cannot do a transaction. The transaction in transferring a coin to another bitcoin uses ETH in buying coins that you want to invest uses BTC, you cannot buy altcoins if you do not have BTC in your wallet the 2 coins are very important.

How much time you should hold from these two.
- It depends on how much time frame you want to hold your coin. Also It will depend on the price that you want to earn.

What is the best time to buy? I should wait for buy right now?
- The best time to buy is when the price of the coin is dump you just have to wait for the price to dump before you buy.