I'm dealing with eCommerce web sites for more than 5 years, I've mostly used standalone ecommerce systems such as Prestashop and Opencart until I came across Mijoshop in Opencart forums about 4 months ago. That was a turning point for me as from that date I build all my sites with Joomla and Mijoshop.
The best thing of Mijoshop is that it brings all the power of Opencart inside the most powerful CMS in the world, Joomla. All of those extensions of Opencart are ready to use. I've one site with about 15 3rd party Opencart extensions and all of them works like a charm. The integration with Joomla is done flawlessly, 0 issues 0 conflicts.
I should absolutely mention about the superb support too. These guys are amazing in timely support and they know they job very very well. I live in UK and I get my questions answered within 1 hour and with proper answers.
In a word, the software is a real dream and the support is very professional, all what is needed for an ecommerce app.