I run/develop ecommerce sites and I have bounced around between many carts. Nowadays I run everything on Shopify. Shopify is pretty flexible as long as you hav

I run/develop ecommerce sites and I have bounced around between many carts. Nowadays I run everything on Shopify. Shopify is pretty flexible as long as you have someone who knows the ins and outs of the API. If you are paying a developer, I think Shopify would be the cheapest to get quality work since the API is pretty well documented. For a while I avoided Shopify because their checkout page was under their domain but I took the risk and it didn't really affect the conversions. The only case I've seen where Shopify wasn't customizable enough was for a site that needed major user customization(custom designs printed on goods). There are plugins for it but it didn't meet the business needs of the product being sold. I would avoid Magento at all costs. It's a major headache to develop anything custom on there. The documentation is terrible. IMO Magento has their own way of doing things so it has a bit of a learning curve development wise. I wouldn't go WooCommerce also.. You might as well just use Shopify and not have to worry about anything server side(hosting, ssl cert, mail server, etc). If I had to pick a open source cart for customization reasons, I would go with Spree Commerce which is written in Ruby. It has pretty good documentation.