The Best Site for Custom Printed Items?

What is the best site one could use to print different kind of items and sell them through Shopify using paid advertising - FB, Pinterest ads and so on?

The site would preferably have print-on-demand option, would ship to all the english-speaking countries, or better yet - worldwide. And it would have differet items - hoodies, mugs, pants, hats, scarfs, pillow cases, bags, phone cases, etc.

Thanks in advance!

Stick to worldwide, theres a huge demand of custom prints .