Used both and off the bat found Flask breezy and Django bureaucratic. But then the next day with Flask you look up how to do something elementary like login (for fsck sakes) and find there's alternatives of various qualities and scopes, and the flask-security guy has disappeared. Found myself spending a full week up front wrangling tokens and other crap instead of the project at hand, sigh. Django starts to shine at that point.

Lately I've been yearning for a "Flango" distribution with flask and the top twenty extensions supported by a single dev team.