Really depends on what you're trying to do and what your needs, skills and budget are.
WordPress/WooCommerce - easy to get going, has a decent plugin ecosystem, plenty of themes with WC support, but struggles to scale without some serious help.
Drupal + Commerce - if you can get Drupal going, you can get Commerce going - it's not as easy as WP/WC, but it's not rocket science. Fewer nice theme options out of the box.
Shopify - SaaS offering that looks pretty neat and if you're not doing anything too wild in terms of products, or you have a suitably capable dev on tap, you can do quite a lot with this. Better for more conventional stores and where you're not doing anything too out there in terms of product bundles or composites or things like that.
Zen Cart - it's open source, pretty fully featured but not great to style, and looks dated.
Magento - the grand poobah. Can run basically anything. A bit leaky, so you'll want a full dev team on hand to manage it. Good luck getting it running.