Both frameworks are full of testing features. The list of features is quite similar in both frameworks. Here are a few links you might check out the list of relevant features:
I choose TestNG because of a feature which JUnit5 is currently missing
Group TestThis feature let me group my i.e. integration test together and let them run in my master build. With TestNG I could also do a before or after group and initialise my test group or cleanup after group run.
With JUnit5 we got something called Tags. Tags are good for grouping tests together. Let's see if they implement more in this direction in future.