We were using JUnit 4, but we had some problems with test grouping. For integration tests we had problems with running order. We had migrated to TestNG in February 2016.
Now we are starting a new independent module for our project and part of our team players wants JUnit 5. I believe it is much better than 4th (there are some new important features, but I see some problems too).
I do not want to use JUnit 5 because of fear of possible problems in our new application, because I have experience with 4th. But I have to be more flexible for the team, so before making a decision I need recommendations from users who have experience with JUnit 5.