Search engine for Drupal site, Apache Solr or ElasticSearch? Hello Drupal community,

I'm facing a issue for a new site that i'm developping. I need to implement a search engine and don't know which search engine to use between Apache Solr and ElasticSearch. It's the first time I do such work and I am desperatly in need of feedbacks from people who used it in there website and who can tell me the difference it makes in a Drupal site.

Edit : I want a new one to display a search bar in the front office to index all the content of the site in a special way. I also want the results to be displayed right away.

Thanks in advance.
Use Apache Solr.It has every feature you dream and the searching is super fast.It can search through pdf as well. As per your requirements I suggest to use Apache Solr. It can be easily done with it.