Tornado is a different animal -- it's asynchronous so when you write code for it you have to program using callbacks rather than in a traditional style.

My current project requires real-time/always-on connections so I started to develop it using Tornado and then decided to switch to the Quora model -- use a traditional Web framework like Flask for most things, and connect back to Tornado for the real-time stuff.

When I switched to this model, the development process sped up considerably. In addition to just being really-well designed, Flask has an amazing debugger that makes me more productive, and it's easier to write unittests for Flask because you can write them in a traditional way and don't have to contend with Tornado's IOLoop.

For real-time stuff, you could forgo Tornado all together and instead use gevent to deploy your Flask app (http://flask.pocoo.org/docs/deploying/others/#gevent), like some have done with Django and Pyramid, but I haven't tried this yet.

You don't need to write tornado in an async fashion. You can use it like you would Flask, but its got a more similar feel to web.py than Flask.