One of the businesses I am currently involved in creating custom tees. My focus is selling them on Amazon, but I have them listed on Teepublic and Redbubble as well. The thing is, on Amazon, I anticipate rotating designs, so shirts you can buy there one month, might not be available the next month. All designs I create will always be available on Teepublic and Redbubble. Another issue is that my shirts for sale on Amazon do not offer some of the larger sizes that can be found on the other two sites. So if you are a bit larger, you'll have to buy from them. Lastly, I only sell shirts on Amazon, but if you go to the other sites, I sell mugs, clocks, comforters, and a bunch of other things.
The link to my Amazon store is http://amzn.to/2tdiEuC
The link to my Teepublic store is http://bit.ly/2sVibe8
The link to my Redbubble store is http://rdbl.co/2teCje1