Being a participant in the cryptographic market is a part-time job, so I think long-term investment is a smart decision. I will choose the potential e-currency and buy them at low prices. I will wait when their price is high then I will sell for profit. I have good income when following this strategy!
The long you hold the coin the bigger chance of gaining more if you're holding the right coin. For me it depends on the coin you're holding with, because holding too long can end up cathastropic loss if the coin that you hold suddenly collapse. So be smart in choosing coin before deciding to hold it for long term.