This question has been asked million times but by the time companies upgrade their services and to make their competition work they listen to people who ask this question, as those people are the ones that analyze each feature to understand the efficiency.
The answer for this question starts with depending on what exactly do you want. So to make it easier for you to decide which CMS to take the best decision is to write down each feature that you need. Also take into account how many products do you have and will the number increase or it will stay the same.
After having the list of features that you need go through each CMS:
- WordPress + eCommerce
Shortlist from the list above to see the difference between 2 CMSes in order to make the decision easier.
There is one news that may change your decision making about Shopify. You will be able to sell your products in all Google shopping channels if you use Shopify. By the way Ecwid also has the same feature. The only problem with Google shopping is that it is available in some countries not all. Check the list out 1st before making the decision.
There is a discussion around this topic in stackoverflow. Check it out Which is better for an online store, Shopify or WordPress + eCommerce?