You name the POD site and I've probably tried it at some point. I started out with Cafepress about ten years ago and did well. That was OK for a while until they changed some of their rules that did not favor creators so I closed up my shop there.

That's when I discovered Zazzle. I've had the most success there but not as much lately. They've also introduced some silly features that have artists spending more time chasing their tails instead of working on designs.

I had a store on Printfection before they decided to stop offering online stores to users.

I had a Canadian POD store on T-shirt Monster. It shut down and became E-store Monster which also shut down.

I had another Canadian POD store on Wordans before they too decided to stop offering that service.

I've got one on Society6 that has made me a few sales.

I opened one recently on Spreadshirt that hasn't resulted in any sales so far.

I opened one at Teespring a couple of years ago but haven't made a single sale from it yet. I wish I could make a sale there because they have the best profit margin after Amazon Merch.

I have a store on Redbubble that has done very well for me. Stickers sell really well on there.

The new kid on the POD block is TeePublic and I'm seeing some good results with them. They have the best profit margin for $20 t-shirts and have an easy to use referral program. If you're interested in opening a store there, let me know if you'd like to use my referral code.