Unlike our frontend, we chose Flask, a microframework, for our backend. We use it with Python 3 and Gunicorn.
One of the reasons was that I have significant experience with this framework. However, it also was a rather straightforward choice given that our backend almost only serves REST APIs, and that most of the work is talking to the database with SQLAlchemy .
We could have gone with something like Hug but it is kind of early. We might revisit that decision for new services later on.
You should go for Responder: asyncio, marshmallow, swagger out of the box. You do not have all the flask plugins, but we have our own oauth, simpleaut and token auth decorators.
No more apache wsgi :-)