I personally have not encountered any significant drawbacks compared to JUnit.
At the start of a new project, my team switched to TestNG and had no regrets. TestNG is more powerful and supports broader usage than unit tests.
Some tools support JUnit but not TestNG. These are tools that I have not yet needed. For example:
- Google's CodePro Analytix supports generation of JUnit unit tests.
- The Eclipse IDE for RCP development supports run/debug configurations for "JUnit plug-in tests."
