First, I don't intend this to be a flame war, please. Python
and Ruby are the only two languages I'd willingly work in
(at least amongst common languages), and TurboGears and
Rails seem roughly equivalent.

I'm much more knowledgable about Python, but that's a minor
issue--I've been intending to learn more Ruby anyway.

Here are the pros and cons that I'm aware of and consider
important:

Turbogears:
+ SqlObject allows working with the DB tables without
using SQL itself.
+ Likely to be faster because as far as I'm aware, Python
is significantly faster.
+ Easy access to other libraries (such as the Python
Imaging Library) that Ruby, being a relatively newer 
language, doesn't have equivalents to.
+ Built-in default SQLite makes it easier to set up?
(as far as I can tell, Ruby requires MySql by default--don't
know how easy this is to change.)
+ I find the templating system somewhat cleaner; code in
py: xml namespace allows pure .html templates, instead
of equivalent of .rhtml files.

Ruby:
+ More mature system. More stable? More features?
+ Much better documented. This is a biggie.
+ Built-in Rubydoc system would make documenting the
system easier. (IMHO, developers almost always
underestimate the need for good documentation that
is written along withe the system.) Is there a
Python doc system that has received Guido's blessing
yet? D'oxygen would seem an obvious choice.
+ Better coordination with Javascript helper code?

I was initially leaning towards Rails due to maturity,
but the most recent version of TurboGears seem to have
fixed a lot of the "ad hoc" feeling I got from previous
versions. But I'm still very much up in the air.

Thanks,
Ken

P.S. If I wanted to provide an image by streaming the
file data directly over the connection, rather than by
referring to an image file, how would I do that? I'd
like to build code that would allow images to be assembled
into a single-file photo album (zip or bsddb file), and
so can't refer to them as individual image files.