Google App Engine or Django?

Google App Engine is an infrastructure on which you can "build and host apps." Though not a web app framework itself, it does provide a simple web app framework called webapp (partially built on top of another framework WebOb).

There are numerous, detailed posts on choosing a Python-based web app framework:

• A similar SO question: Django vs other python web frameworks
• List of Python-based frameworks with short descriptions
• You can learn a lot about what makes up a web framework and what options are available in Nick Johnson's excellent series which starts with Writing your own web framework for App Engine