Hi hulk,
Not used virtue mart. OsCommerce is O.K... or atleast, it was in its day.. its well known for leading open source ecommerce for quite some time but that was years ago and oscommerce is no longer actively developed. Its prone to malware attacks. As a web developer, I've repair/recovered several oscommerce sites in the last year that have been attacked and are now out of date, and thus not all that suitable for large scale online retailing.
opencart is good, and quite straight forward. Magento is awesome interms of scalability and its "app" (Magento Connect" marketplace offers tens of thousands of extensions to your store. Magento does however come with quite a learning curve as far as development is concerned. Prestashop is another good one, quite simple.
Both Magento and Prestashop have online hosted versions that are easy to setup and administrate. Both are paid services though.
Good luck,