For gardeners in mainland USA I suggest 10 inch by 20 inch trays(1020 standard). You can have 36, 50, 72, 144+ cells that fit in that footprint as well as 4 packs, 6 packs, 18 pots/tray, 8 pots/tray, 2 pots/tray and probably many more options. You can also find 10x10 inch trays and jiffy/coir...