I have chosen to grow most of my plants in flat trays, with a size of about 50 x 30 cm. They have a sieve bottom, which I cover with root cloth. That way the plants have a certain amount of space around them, and a reasonable size of growing medium. This does not stop the plants from growing into the tray of their neighbour!
Some of the larger plants arge grown in big, 10 liter pots, because they probably get too big for a tray. Species like engelmannii, scheerii and bergeriana just grow too large to put in a tray. I leave a fair amount of space between the pots, but even that is sometimes not enough. I should probably grow them in the ground, but some of the plants will get massive than, and my greenhouse is not that high. Maybe in a few years.