Currently 3 search engines exists :
eZ Publish Platform 5.4.5 and higher, Solr is the recommended search engine for production use of the API. Currently Elastic Search is experimental, not professionally supported, and won't be made stable anytime soon.
Note: Solr Bundle does not support advanced search features like out-of-the-box facets (making custom facets is possible), spellchecking and so on, for that continue to use ezfind as those features will most likely not be backported to 5.4 (Bundle and kernel). This recommendation regards speeding up the API as a lot of API interactions is using search api, which gets more stable performance when running on Solr.