potting

What's the best potting to put your plants in to? I picked up a bunch of 12'x12' square plastic ones. Then I realized plastic emits a toxin. Maybe that's not so good for plants. I remember some guy in winnipeg was making them out of horse shit. Prolly the best but I seriously doubt they'll be easy to find. So what's easy to get, and perferably square?

you could use ceramic square pots, I have seen them at almost any gardening store or gardening section at walmart, lowes, home depot and some others. They are sweet