What are the best resources of ITIL and how to know which version should I use for example if two versions are available?

If you are totally new to the subject, go to the latest and most recent version.  However, if you started your journey with ITIL/ITSM at a prior version/release, then take the upgrade/migration path from that version to the most current one. 

As for resources, it depends on what you mean by this question. The best resource - generally speaking - would be the official literaure (ITIL Library) by OGC if you talk about something else, then let me know !!