So here is a real quick break down from my experience of 5+ years on Shopify and 10+ years with WordPress.
As many have said WordPress has likely a larger pool of developers and designers for you to pull from if you are hiring out the development of your site and therefore probably would allow for slightly more customization and easier design changes along with potentially lower costs. And there is nothing that you can't do in WordPress that you can do with Shopify - just a function of how easy / hard it is to get it done.
Along that same line of thought Shopify can be very easy to set up IF you are happy with a theme "out of the box" then you can be up and running in a day or two. If you are hiring out the development we have found that there is a smaller pool of developers who specialize in "Liquid" which is the programming language Shopify is built on. Can you find developers who are awesome in Liquid/Shopify - sure - but it will typically cost you a bit more as they are a tad harder to find and are usually in high demand.
Two ends of the spectrum - where each in my opinion are clear winners....
Quick - Up and Done... Shopify
So if you are looking to get set up and running in a week and you will be "OK" with picking a stock theme in Shopify and running with it to get an ecom store going - then Shopify is your winner by a mile.
Got Time - Very Particular on Look / Feel / Need to be in clear control of pages on an ongoing bases for UX or SEO changes.... WordPress (or even Magento)....
As you move towards the middle then the arguments blur a bit between which is absolutely or clearly "better"....
In the end both are totally awesome -
Hope that helps!! Best of Luck in your new adventure!!