It depends on the altcoin and how much is the profit you want to get before selling it. But for me most altcoins are not good for long term investment (not all) because of the pump and dump and the whales that are manipulating the market, that is why I prefer short term trades when investing in altcoins, so that I can buy in dips and sell when it gets pumped by big investors. But it is still depends on you, if you think that coin have a potential to survive in future and can grow more then do it (it can be more profitable), because cryptocurrencies are speculative investment.