I am new to implementing site search feature in our site in AEM, it should have autosuggest feature,fast and should be able to search in documents also apart from content in site, can anyone suggest me the possible approaches for this, and how much is it benefitial to implement any external search like ElasticSearch in AEM
I see this posted in 2017, Try using Elastic search as a service, it provides dashboard and provides trial version to explore all the options. Here you have a look at the setup for Elastic search as service.
Also you can have a look at the Algolia Site search Which I found really awesome to work with. Happy coding!!