Elasticsearch gained its popularity amongst developers by being enjoyable to use. A simple feature comparison against it's competition doesn't convey the significant advantages of just how easy it is to work with. This is due to multiple design choices such as the use of JSON for the API and queries.

Another useful and unique feature to Elasticsearch is the ability to have multiple types of documents in a single index. You can then facet, query or filter against all document types or a single type.

There's a 14 days-long trial available without any credit card required.

This is the official version of hosted ElasticSearch and it's backed by the ElasticSearch developers. This makes it probably the best in terms of stability as far as services that use ElasticSearch as a backend go.

Since this is the official hosted ElasticSearch, the latest version is the one that's always in use.