If you want to hold for long term a little diversification on your portfolio isn't that bad, I could recommend ADA and EOS, but the majority of altcoins are more suited for short term.
I think if you want to diversificate your portfolio, you should buy BTC and ETH primarily, and then you should think about other tokens and coins, such a EOS, Waves, OmiseGo, Qtum, etc. But its a problem if TS bought any coins in January,2018.