Choosing an elasticsearch version

Currently, we are using elastic 5.4.
We want to upgrade it to the latest stable version possible.
What is the most recommended and stable version currently? (6.8.2,7.1.1, 7.2.0)

Versions which are GA'ed are stable releases. You can refer to past releases and release notes here.

However, we always recommend all users to upgrade to latest GA'ed version (7.2 now) as it has all the updates and new features.