Both are good but I think short term is little bit better than long term.Because when you purchase a coin at low price and sell it at high price and if it will continue I think your balance will grow up.but after a purchase if you hold it for a long peroid it can also give you profit but ratio may be litte rathe than short term formula which I mentioned.
In my opinion long-term investments is the best option. The more money you invest also, the larger income you will have. If I choose long-investment strategy, I deal with NEO and Ethereum. ARK is also not a bad choice.