Cryptobreakdown is an website which aggregates discussions on a few forums and uses machine learning algorithms to extract relevant information about how those currencies are perceived at different moments.
Sentiment analysis could be a good indicator to decide when to invest in currencies, but usually it can not be used by its own, should be correlated with other indicators.
They also provide a second page where you can compare the sentiment analysis for 2 coins and you can follow them on twitter to get updates when trends are switching.
