Printify: Print on Demand

Pros:
Soooo easy to design and use--probably easiest one out there
Super easy to update products--very logical
Review system is broken down nicely so you can decide what's important to you in each individual vendor--love this
Good job of letting you know when stuff is OOS
Good spreadsheets and reports
Lots of vendor options
Responsive customer service at all hours!

Cons:
A little more expensive than some smaller vendors (if you search, you can find better deals!)
**Overrides Shopify's fulfillment settings. Unless you have Printify also set to manual, they will make your stuff, even if you don't send the request from Shopify yet and have manual fulfillments set up in Shopify. no other app (of the 7 we work with) does this--so be aware if you prefer to do things manually or partially manually within Shopify.