All coins mentioned are very very good. But if I were you, I would invest in more than one coin. They say it is not good to keep all the eggs in the same basket.
So it would be better to choose a number of coins and split equally your money to them. Store them in paper wallets keep the private keys safe and just forget them.
Be sure you make a plan on how long you want to keep them and don't be tempted to sell them.
I am confused to determine which altcoin I will buy to keep in the long run, do you think?
Ofcourse if you plan on investing for long term, id suggest you better invest to trusted crypto and to the crypto that has big potential. So id like to recommend
1. Btc
2. Eth
3. Ltc
4. Neo