What is your best size container for figs?

My best size containers for figs were 20 gls, now 15 gl squat. Use the same way of growing figs. Figs has invasive root system so it does not hurt to do bigger than normal pruning. I usely leave a third and hollow the centers a bit, also cut-out wedges. The containers i prefer have large square drainholes, no issues with drainage when roots are coming out of them freely and going into the mulch around the container. I also dig a hole about 2" deep for the pot to set in. I have strong winds here and big tree’s get blown over easy. When you set the tree in your new container, round the center up towards a bit so it confers to your root pruning.
The sooner the roots go in the ground the better, the tree will grow much faster, better looking tree’s and fruit by far.