Django is a mature and highly regarded Web framework that assumes you know Python well. Its libraries provide a good selection of the must-have capabilities for accelerating Web application development: an object-relational mapper so that you don't have to write your own RDBMS interface code, a template system so that you don't have to wrestle with marrying active Python content to static HTML content on a Web page, an administrative interface so that you can easily access your site's back-end data (as well as easily manage website users and permissions), and so on. You should expect to spend a stretch learning Django's API, but the time you put into Django is well worth it. It's a rich environment with much to recommend it.
CubicWeb touts itself as not merely a Web development framework, but a semantic Web development framework. This distinction becomes clear when you discover that a CubicWeb application's interaction with a database is performed through RQL (Relation Query Language), a query language similar to the W3C's SPARQL for RDF. CubicWeb's libraries translate RQL queries to SQL or XML or LDAP or whatever protocol is appropriate for the data store being accessed. CubicWeb is probably the most difficult framework in this review to grasp. The difficulty is not only on account of the jargon you must learn, but also because constructing a CubicWeb application entails lashing together modules (called cubes) into a final structure -- a process that will be foreign to neophytes. Once you get the hang of it, however, CubicWeb does permit rapid development. A basic model schema is enough to get an application off the ground, and CubicWeb's agile characteristics let you grow the application in iterative fashion.