It seems like the best time to sell altcoins is over, as we know that the best history of altcoins is 2017 until March 2018, almost all altcoins prices go up because they follow the trend of bitcoin prices, now we can only survive and wait for a miracle.
I still believe that such time would arrive again, because the market runs always in cycles. Sooner or later we would come to the point when BTC dominance would fall and leave space for altcoins to grow.