Well here i my 2 cents. Drupal runs some major ecommerce sites in terms of traffic. Joomla is ok, just not my first choice. Wordpress has a lot of ecommerce options, but if I was using Wordpress, I would ue it as a front end with opencart as a backend.
A lot depends on what you want. If its a store, I would look at opencart, oscommerce etc. I have a oscommerce store with 300 products out of 900 in the top 30 posistions with no seo work.
If its a customer adding products/etc opencart and/or wordpress is cool.
If its a ,amaged setup, drupal is a great option.
Hope that helps