I've used virtuemart, hikaship, oscommerce, prestashop and various others. J2 Store is the simplest, intuitive cart I've used to date. If you want to get your products on sale quickly and have the freedom to design your product pages with complete freedom, I would advise using j2 store. Also there paid service is well worth it because their customer service is top notch. They answer your questions and give you solutions right away.