My ill informed opinion: the WSGI specification (i.e., PEP 333) together with a decade or so of cross-pollination seems to have made most Python web frameworks more similar than different. You can opt for more out of the box functionality at the expense of less flexibility, but not much else. (The exceptions seem to be where the code is really old and/or asynchronous.) Django seems to be the BDFL blessed option.

Example: Everyone seems to think that Google copied "their" Python web framework in creating the "webapp" framework for App Engine. webpy, Django, ...