I sold most of my altcoin holdings for either Bitcoin or Ethereum in 2018, and that was one of the best investment decisions I made with cryptocurrency. I was having dozens of different altcoins and tokens, such as BSD and TMT. After I sold them, the prices declined for most of these tokens (in some cases by more than 95%). I still have a few alts in my wallets, but they now constitute for less than 5% of my portfolio.