We chose the A3 portrait print option for our t-shirt design. We recommend choosing the printable A3 or similar sized canvases if you ever decide to print the images.
If you start creating a t-shirt design which doesn’t use the correct print options, then you are only limiting how you can use this design. Non-print ready files are limited to online use. They can be printed, but in most cases, the quality of the image will be so bad that you will see small pixel squares.