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.