Someone else mentioned JasperReports which is probably the best choice
if you already have reports written or would prefer to define your
reports in XML. Ruport is a pretty low level toolset, but many of our
users are pretty happy with it, especially because we make integration
with ActiveRecord pretty easy via acts_as_reportable.
I would not recommend using PDF::Writer directly for anything at this
point. Even if you don't use any other functionality in ruport, our
Formatter::PDF adds interface improvements while fixing a number of
serious issues in PDF::Writer at the same time. Most of these patches
came from Austin, but do not exist in the released PDF::Writer code.
(Memory patches, bug fixes, etc)
It really depends on what you're trying to do and how much you want to
roll up your sleeves. Searching through the Ruport archives for Rails
might prove helpful, and if you have any questions, just let us know
on the list. (http://list.rubyreports.org)