Definetly long term is the best way to invest in cryptocurrency, i do hold coins almost 3 years and its the best decisions so far. DYOR is the best advice before buying coin and also you should not following hype and stay away from coin which promise you to the moon without any solid reasons.
If you have extra money, you can buy coins and hold long term. No one can guarantee the profit if you hold long term. That's why you must choose good coins. Because if you choose the top coin, you are more likely to make a profit. However, you can still earn enough profit by day trading.