The best is the one that meets your needs. It usually best to use a WAMP or XAMPP or MAMP localhost setup on your desktop computer and compare them side-by-side - setting up your store and theming the site.

I have a list at showcasecms.com/ultimate-cms-guide/the-list (bottom of the right column) that has a half dozen links to ecommerce system sites.

~silverwing