Both these search keywords would tell you Shopify or Magento but what they don't say is how to create a subscription-based eCommerce business model or which is the best online store approach when making your decision. Is it flexible for a fully customizable eCommerce business that is scalable, yes but at what cost? 
Make sure to ask yourself these questions, 
Is your subscription e-commerce business model simple?

If your type of subscription model is simple, then we suggest you choose Shopify or Shopify Plus, but if you required complex features on your app that allows users to subscribe to a different type of products or have an extensive inventory of products, then we don't suggest using Shopify. 

We recommend that you go with a custom open-source platform that can be fully customizable with no annual fees.

Does your business plan involve spending in growing your business within the organization?

If you have plans on growing your business and if you plan to hire internal developers or web designers in the future as part of your eCommerce model then we don't suggest using Shopify

If you are serious about starting a business that can potentially grow, make sure to consider pricing. Unless you are running a small website, expect to pay and for Shopify Plus the absolute minimum fee you are supposed to pay around on top of any plugin you might be using, you can expect to pay approximately $29-$299 to $2,000 per month.

If you choose to go with a fully customizable eCommerce open-source platform for your subscription business, you are expected to be paying $0 for Annual License Fees and around $50 per month on a dedicated server that can auto-scale, this pricing is just an estimate that is base on an average depending on usage. Just know that you will only pay for what you use.