What you should buy depends on your market and farm needs. Does that help?
Do you need large bulbs or would medium size bulbs sell better at your farmer’s market? The jumbos are great for efficiency and eye appeal, but can you get what they are worth per pound? You get a lot of planting stock per pound when buying medium size, but do you want to handle 10+ bulbs per pound versus 4-6 of the jumbos?
The picture has three sizes. Medium on the left, average size large in the middle, and a jumbo size large on the right. I like to plant from average to large size seed stock. Somewhere between the two big sizes. This maximizes cloves per pound while maintaining large bulb size. If I sold for market I would probably settle for an average large to medium size bulb.
There is some disagreement on just how much bulb and clove size affect the size of the bulbs you will harvest next year. In my experience the bigger cloves from the bigger bulbs bring you a bigger bulb the next year. There is some ability to increase bulb size in one year but it is incremental. You may get a medium to bulk up to an average size large in one year with good fertility, but you cannot get a small medium to a jumbo no matter how much compost and magic growing potion you put on it. There is also a bit of diminishing returns on the high end though. If you plant a 3 inch size bulb don’t expect to have all 3″ size the next year.
There is also a thought that smaller bulbs store better. I don’t have much data to back that up but in my experience it seems to be somewhat true. However, if storage length is a priority for you I suggest looking at planting a softneck which is a longer storing variety. Also, increase your soil health and nutrient density of your garlic and you will get longer storage.
Any other questions on bulb size or other garlic growing tips feel free to contact me. – Darren