Short-term investments have fewer risks, but they give less profit. Long-term conversely give more income, but also more risks. I like to combine both options. In a portfolio with long-term investments, I have tokens of various promising projects and coins purchased at the ICO.
I think the opposite, short term investments are more risky than long term investments. Because, in general form, the market will be bigger and all the coins will provide you profit in long term. Instead of short term investment, I would do trading on the exchanges.