One of the things I like about browsing the Web for posts on various CMS topics is that they always seem to show up on the Web when when I need them the most. For example, I'm starting to consider whether I'll continue to use osCommerce for some sites that I manage. While the yet to be released osCommerce 3.0 will likely be an option next year, I'm open to other possibilities. What I would like to see is a shopping cart that integrates well with a full CMS. In the past, I've found Joomla's Virtuemart extension and Drupal's e-Commerce module to fall just short of the client's needs so I've stuck with pure shopping carts such as osCommerce. Yet, I still keep on hoping for better open source options.
A new shopping cart module for Drupal, Ubercart, is hot under development and attempts to address the short-comings of the Drupal e-Commerce module. Ubercart's roots comes from people like you and me who wouldn't mind moving the client from osCommerce over to Drupal. In fact, some of the user interface in Ubercart is very similar to that found in osCommerce (check screenshots), which is a good thing for clients to experience during a migration from one application to the next. Ubercart is still under alpha development, but if you've followed osCommerce's long software development cycle the terms alpha, beta, and release candidate are not terms that will scare you off from taking a look at Ubercart.
So here I have a need to see a comparison of Drupal's e-Commerce module and Drupal's Ubercart module. The Web gods smile on me and provide me Brenda Boggs' recent comparision of the two Drupal shopping carts, "Diving into Drupal E-Commerce: An Ubercart vs. E-commerce Comparison".
So, for all these reasons when an e-commerce site fell into my lap a couple months ago, I chose Ubercart.
Another project came my way shortly after which used a variation of modules that led me to believe e-Commerce was the way to go, plus I wanted to know how well it held up in comparison - so for that project, I chose e-Commerce.Having worked with both in overlapping time frames these past few months, I've got a pretty good understanding on how each works, the differences between them, the pros and cons as I see them, and community behind them, yadda yadda.
As far as I know Brenda Boggs' post is the first independent comparison of the e-Commerce and Ubercart modules. As a commenter at her site suggests, if you're using osCommerce and another flavor of osCommerce, such as ZenCart, Ubercart would be a good module for you to take a look.