Personally, I'd stick with BigCommerce. They've finally listened to their customers by implementing changes and they've just recently released version 6. Although, slow and some of the features are somewhat outdated, they're still monitoring our requests on which features should be implemented.
I personally use Ubercart as a bolt on module set for the awesome CMS Drupal. This is because Drupal gives a lot of flexibility as a CMS with advanced features being only a few clicks away such as a blog and forum etc. Then the power of Ubercart finishes it off nicely.
I prefer most joomla-virtuemart for ecommerce website. You may check my website 99desires.com which I created using joomla virtuemart.