It depends on your coin, if it is a good coin, then keep it. One time it will double its value. If you are holding a newly hatch with low level coin, dont hestitate to sell it or you will end up lose in trade.
Definitely you need to dump the coins that has new future to increase the price. Because there are a lot of shitcoins and you must choose the coins you want to invest otherwise you will end up losing. So hold for good coins and dispose others that have no value at all.