in my opinion, the best altcoin currently only has 1, namely Ethereum. you will not regret buying it, because Ethereum is very useful as a tool for future transactions, and investing for the long term is very good
well ethereum as it self are to be the best altcoin for top 10 if you just based there is other too like litecoin and anything else but always check for the project and not to be taken easily that this is could ever be made you to be more good in trading. Choosing for the best altcoin are depends on you.