In most cases it's just a matter of preference. Elastic has some extra tools like kibana an was more focused on having statistics and aggregations working well,

In most cases it's just a matter of preference. Elastic has some extra tools like kibana an was more focused on having statistics and aggregations working well, while Solr webui is a lot more complete than the elastic one and the full text search and relevance bits are more explained. Internally both use lucene, so you are going to be able to do the same things with both. I worked extensively with both and I prefer the way of administering Solr. Anyway I use Elastic when it involves logging and statistics thanks to kibana.