I think that should pay attention primarily to the coins that have already proven themselves, namely from the Top 20. I like Monero, Zcash and NEO. Can also pay attention to new projects. For example, on Zilliqa and Quarkchain.
How has Quarkchain proven itself? It was only released a few months ago. Definitely one to watch for the future, but I wouldn't say it's anywhere near proven.
I think it would be best to watch high potential coins rather than already proven coins if you want to see explosive growth.