It's really hard to say. Actually each theme has its own strength and weakness. Before you asking what is best free Shopify theme, asking your self what is your bench mark for a best free theme?
To my opinion (of a growth marketer)
Free (of course)
High conversion rate - most important. It may has built - in features such as trust badge, product page countdown, real time purchasing notification and other function to boost sales.
Good blog for SEO & be able to sell from those traffic
Hi everyone, I prefer some responsive websites, I have to say. There are some nice premium shopify themes www.templatemonster.com/shopify-themes.php which you can use for such a purpose. I think you guys will like those themes for your projects too, good luck ;)
