Magento would be the obvious first choice due to it's unprecedented flexibility and control options, as well as wide community, free extensions and translations. Although, admittedly, earlier versions did have some performance issues, these can be solved with appropriate optimisation relatively easily and I wouldn't generally worry about those.
If you e-store requires more complex content management solutions then VirtueMart (Joomla shopping cart component) is another product that you might wish to consider. It has all the features of major e-stores, as well as multi language support and free translations to major European languages. Their website can be found at virtuemart.net, and I believe that it can definitely be an excellent solution for more complex projects.