Deciding what is better is a vague concept. Better is what aspect? We cannot say something is better than the other in general when both sides have ups and downs. We can only say that the other is better based from our perspective depending on a specific situation.
Long term investment is better if you do not want to monitor the market often. You just buy coins and then check the market whenever you want. There's no hassle for you since you do not need the money you invested. Short term investment give more profit than long term but you have to monitor the market more often so that you can decide when to buy or sell. It requires more work but worth every effort.
So based from those comparison, decide.