The best ecommerce platform is the one that does most of the things you want, and offers the the easiest (and reliable) way to do it. Choice also matters at what stage the business is at, current sales volume and expected growth. I personally prefer woocommerce for wordpress for most of the work we do, some of the reason is knowing how it works and how to do big things quickly (imports, updating in bulk etc). Some people wont like woocommerce, for some it wont do the job required, but for most webshops it will do the job more than just fine, and there are plenty of addons to get the functionality required. I have found other ecommece systems like magento, prestashop, opencart to be not very user freindly and fall down on many aspects of theme customisation, also the addons seem to be rather expensive so if you need customisation the cost goes up considerably.