What is the best ecommerce platform?

As the title says, just wanted some opinions on what is the best platform for ecommerce?

I am talking about a medium sized store (roughly 5k products). I want speed, security and functionality.

I know Magento is well known for running big ecommerce sites, I know its very functional and can connect with a lot of other platforms BUT its also complicated and its got a lot of running costs in my experience.

Shopify I have heard good things but I don't really like platforms where you have so…

What is the best ecommerce platform?