Getting a shopping system on WordPress is easy to do -- provided the plug-in is compatible with your site. I had initially tried to install the WP e-Commerce plug-in, only to find that it would not install onto my WordPress site. It may have been the newness of my WordPress version that was throwing the plug-in off.
Daunted, but not stopped, I moved to eShop, which installed quite cleanly. eShop adds its own configuration screen to the site's Settings menu, so it was easy to access the controls to configure the catalog.
I was impressed by the depth of control and the way the plug-in fit in with the existing site. It took a little bit of effort to discover how to add products to the catalog, but once learned, the workflow was easy to do.
This one is close to call: I have to give props to tools like Ubercart for the completeness of its features, but JoomShopping and eShop made it easier to build a product catalog.
I think I have to give the nod here to Ubercart. Like the Drupal CMS, the learning curve is higher, but the long-term payoff is a better overall experience.
Near the beginning of this article, I mentioned that all of these CMSs have very vibrant and active communities. I wasn't kidding. To give you an idea of what kind of ecosystem we're talking about, there are 15,884 WordPress plug-ins, 11,216 Drupal modules and 8070 Joomla extensions available at the time of this writing.
It's not all about the numbers, though.
Drupal, being the older product, has a larger and more active developer community. This is certainly reflected in the number of modules, but it also shows in the support for the CMS. The Drupal website has a very good modules directory and solid documentation.
Oddly, when searching for help on some Drupal issues, I was often pointed at sites other than the main Drupal site. This is too bad, because there are some good docs in there.
A majority of Drupal modules are categorized as non-commercial, meaning free, something which is different from the Joomla extension family. Free software users will be comfortable with this, but commercial users may need to get used to the lack of commercial support.
What Joomla lacks in numbers, it more than makes up for in energy.
Documentation on the Joomla site is wiki-based, updated constantly and well-indexed by search engines. So I ran into it a lot more often when searching for help.