For now, Ripple and Ethereum are the best altcoins to invest as Bitcoin is following the bullish move and ETH & XRP is about to show some surprising positive signs with it.
They both have huge potentials for long term investment. But i suggest you should study on your own and make some comparison on the coins you think have high potentials. Do not rely much on the forum because you have your own mind to decide and at the end of the day, you are still the only one responsible of your own decisions. So study more and make your own good analysis.
Personally, I don't see any great potential for long-term investment because even when people mention the top altcoins, the value of these altcoins has had a bad time, almost right now, if anyone decides to hold the potential and long term altcoin, they are bleeding and crying with this market. Crypto market has gradually removed the hold method, users need to change the place they hold in a short time, there are no altcoins that are good for the long term, looking for short-term options that will be safe and profitable, but first, we need to analyze everything very well.