You need to measure the public perception of your brand on social media by using natural language processing. Which Azure service should you use?

Text Analytics Cognitive Service could be used to quickly determine the public perception for a specific topic, event or brand.
Example: A NodeJS app which pulls Tweets from Twitter using the Twitter API based on a specified search term. Then pass these onto Text Analytics for sentiment scoring before storing the data and building a visualisation in PowerBI.
Reference:
https://www.linkedin.com/pulse/measuring-public-perception-azure-cognitive-services-steve-dalai
https://docs.microsoft.com/en-us/azure/cognitive-services/text-analytics/overview