[tedmiston]

Depends on your priorities for learning.

Pick Django (+ Django Rest Framework if building an API) if you want to take advantage of its many abstractions, build features and ship fast.

Pick Flask if you want a small, simple codebase that's closer to the metal. You can learn more this way but it also takes more work to ship the same app in Flask vs Django IMO. One example is the Django ORM is much more intuitive and simpler to get started with than SQLAlchemy.