I like the idea of investing in some coin and forgetting about it for three years 
I would agree with forumers, really good earnings are possible only in a long run. You can buy, for example, BTC and hold it. Or you can exchange it for its forks BCH and BTG and try to play with them. Luckily, they all are widely accepted and supported by many popular exchanges like CEX: https://cex.io/bch-btc, https://cex.io/btg-btc. These coins would probibly be the best for a log-term investments.
I would agree with forumers, really good earnings are possible only in a long run. You can buy, for example, BTC and hold it. Or you can exchange it for its forks BCH and BTG and try to play with them. Luckily, they all are widely accepted and supported by many popular exchanges like CEX: https://cex.io/bch-btc, https://cex.io/btg-btc. These coins would probibly be the best for a log-term investments.