I've grown in airpots for 7 years. Photos and autos and I love the pots for a myriad of reasons, but I honestly think they are better suited for photoperiods. You can start seeds/clones in prop cells and then pot up so that root development explodes into the bigger pot. The results are mind boggling! These pots start trees and the owner of airpotusa is savy enough to welcome cannibis growers with welcoming arms.
If you're deadset on airpots I agree with
@Vorkosigan comment above and it's best to choose size according to your set up, but your medium in said airpots will determine the size of the plants in addition to your environment. I use red bottoms with tupur and I can get decent size med to tall plants in those with photos.
For autos I'd say go as big as you can afford and have space for. My growing experience has taught me that the longer that auto taproot has to travel, the bigger your plant will be. I've yet to get big autos in soil with my redbottm pots. Ive grown in all the popular brands of soil including buildasoils modern mix 2.0.
In coco I could grow trees in the red bottom airpots. Tupur is not quite as good as straight coco, but darn sure good enough for growers who can source it. I also have a blue bottom airpot that grows mini trees, but I rather grow my California 6 in smaller pots rather than 1 big one since I can keep my COBs right on top of them for a good canopy blast of PLC goodness. Again these pots start trees so the bigger the better in soil, the smaller the better for coco. I've seen 6ft single cola plants grown in prop cells
only. The possibilities are endless with airpots!!
Sorry for the long post but I try and give insight with details to help you see different sides of the coin and the fun about these plants is that you can keep on experimenting to your heart's desire. I tend to use my Mephisto freebies for experiments so I don't waste my paid for seeds. Thanks again
@Mitch and crew!