Finding a good altcoin is really a very tough job. You need to research about the coin who is behind it. The coin should have a good project with feasible product. The coin should have open codes on github and have a so called roadmap and timeline for upcoming updates. You need to check the previous price history and charts of the coin. Coin have listed on good exchanges and have good volume so you can buy and sell your coins easily.

I would prefer you to have a look on ADA, NEO , NANO , ETH ,EOS , XLM.

Always remember sometimes market will play against you so just trust on your holding and wait for reversal.