By far the best altcoin that I have invested in is Ethereum. The coin has provided with hugh profit gains in the past. Last year its profit percentage was 3700% and with a market capital of $51 billion, the coin still grows strong in the market. I know that the altcoin will be a success by following its statistics in the past and also whether the coin is getting mainstream acceptance or not. Also, I look for the new features that make the alt much better than the other coins and whether its commercial in the market or not.