Actually to examine all altcoin, it will take a very long time. Because to determine the best coin must at least do research first. Recorded the number of coins in
https://coinmarketcap.com/ there are about 1373 coins today. But to take a brief i just see or do research on the top 10 coin in coinmarketcap.
The first best coin for me is Ethereum, i'm interested in ethereum because have a stable price, compared to other coins that can go down in price very drastically. For example is, bitcoin cash, from the $2500 price could go up to $3500, and otherwise from the $ 3500 price could drop to $ 2300. But not for ethereum, until some time this price is stable at $750.
I thinks that all, although there are still many coins that are potential, especially for investment.