Okay. So I'm biased because I'm the author of Flask, but here something to help you make the pick:
- itty - very minimal framework, Bottle is probably a more stable alternative if you want a single file installation.
- Flask - new and actively developed, shaped similar to Sinatra but also differs in a few points. Large number of extensions for SQLAlchemy, CouchDB and more.
- Juno - not updated for a year. Usually not the best sign.
Besides the ones you mentioned there is also Bottle which is similar to Flask but more minimalistic. Unlike Flask it also re-implements everything from ground up instead of building on an independent foundation like Werkzeug.
Other alternatives is web.py, one of the first microframeworks ever. Same rule as bottle: re-implements everything from the ground up.
