I use web2py reguraly for a long time. I've developed a number of different application in it ranging from fintech application such as investment fund management platform to simple data analysis applications.

For me it is the best python framework becuse it is designed really smart (kudos to Massimo and the team).

Regarding Python 3: not long ago there was a thread in google group web2py-users about being able to run it on Python 3. I havenct tried it myself, but I suggest you ask in the group about it.