Hard to say which altcoins are the best to hold them for long term? What do you mean with long term. Long term is for me if you hold a coins for 2-5 years or even longer. Good coins to hold for a couple of years are Ethereum, Litecoin, Waves and last but not least Bitcoin! 
Something close to that mate, maybe around 10 years. Im planning to invest my $1000 that I got when I sold my exrn tokens. I am looking for a more solid project that will be profitable soon so that i can use it when I retire from working at the age of 40.