The best coins out buy at this time would be those which are linked to bitcoin because those on the bitcoin blockchain network if not remaining steady in value will depreciate like bitcoin on a low rate and in a bear market the lowest the drop the better hr recovery
Among altcoin, the best coin has always been ETH and Litecoin. Both these coins have been giving away good profits in short term investment and ETH is also preferred for long term investment. Besides, ETH has good price stability and when the market was down and all the coins falling, the average fall in the price of ETH was the lowest than the rest of altcoin. Having said that, I would choose ETH as my first priority and Litecoin as the second.
As for me, Ontology, VeChain, Stellar, Cardano, and Ontology are the best altcoins to buy in August-October. I think, close to November 2018 they will gain. Check these alts as well:
https://www.youtube.com/watch?v=tCXhdx270q4