eBay, amazon and Shopify are all options. another is WordPress and woocommerce, which is my preference.
They all have pros and cons.
Ebay and amazon have an existing customer base so you save on the advertising. Plus you don't pay anything unless you sell. But they both already have a lot of competition which pushes your price down, also there is a lot of Chinese suppliers selling directly on eBay and amazon making it almost impossible to compete on some products.
Shopify, is easy and if you use Oberlo adding products is super simple. But the price is a bit off putting if you are just starting out. The $29 a month plus the marketing costs soon adds up. Also you will probably end up buying some premium plugins.
Wordpress and Woocommerce is a bit more work to set up but you will only have to pay your hosting costs every month. You will still have to pay for your marketing.
I use Wordpress and Woocommerce because it gives me a bit more freedom to set the site up exactly how I want for each product.