The best long-term investment is to invest on low-priced coins like as low as a cent because after a year or 2 years it will be valued into $1 or even higher.
But if you have more money to invest then you could start on Top Altcoins like Ripple, Stellar, Tron, Verge and other low valued Altcoins that will offer you more coins in a single investment than Bitcoin, Bitcoin Cash, Ethereum and NEO etc.
This way will offer you higher opportunities that you'll get higher return after a year or more.