Hey @dichao, good to see another cryptomind around :) I would suggest you to check my other article, where Im sharing my opinion on getting into mining in June/July 2017 and why its the worst time!
For now, I would suggest you to just simply buy and hold!
I can recommend BTC/ LTC/ DOGE.. these are the currencies I've invested into.
It also depend, for how long you want to hold before collecting the profit. On the long term, I believe its BTC. The new cryptos like ZEC, DASH... they are currently hyped based on news and speculations, but where you can actualy pay something with DASH, ZEC, etc.? I think LTC is much better and wider spread crypto already and BTC is the best for "store of value".
Good luck with your crypto-profits buddy ;)