Well, "best" is somewhat based on what your needs are, but there are a number of options out there. If you're looking for something free to start with simple features, Storenvy and Tictail are popular choices right now. I just left Storenvy, as have a number of artists/makers recently, because of some changes in their practices, but it might still be a match for you. I moved to Tictail, which I'm happy with so far. If you have any specific questions about either I'd be happy to answer them. Etsy is a really big name though I think it can get easy to get lost in the sea of sellers there, plus people sometimes tend to say/think "I got X item from Etsy" rather than "I got X item from Seller, who is on Etsy".

There are other store options with subscription rates that may have more powerful tools for customization and such if you need them, such as Bigcartel or Shopify. I haven't used those personally but they are also worth a look depending on what your specific needs are.

Redbubble, Design By Humans, Teepublic and so on are great for selling design work printed on things and getting royalties, but since you make all your own merch, you won't need to check those out unless you decide to branch out into designing for print on demand as well.