Which version of Python ? Django or Flask ? Django ORM or SQLAlchemy ?

There are only two practical choices right now, both for Python 2:

1) Django 2) Flask + SQLAlchemy

Not that much choice, is there?

With Django 1.5 (final just about to be released, hopefully within a week) supporting Python 3, you're not tied to Python 2.

There are other good options, too. Here's one, also conveniently Python 3 compatible:

(3) Pyramid with (a) SQLAlchemy; (b) ZODB; (c) something else—whatever you want!

I'm actually working on a Pyramid + traversal + ZODB project just at present. It's very instructive when once you have become used to URL routing and pattern matching (I've worked with Django hitherto).

I like web2py's DAL