They got some big xxx cabbage in Wisconsin...6 to 15lb. heads of cabbage!
The last time I picked some up for sauerkraut, 3 heads were 40+ pounds. The grower lists it on his web site as kraut cabbage.
Tip 1: The fresher the better. Also heads that are heavy for the size are best. Loose heads tend not to be as good.
Tip 2: Sealing the container with a zip lock bag filled with a salt brine is the way to go. When I was a kid, every one used a weighted plate and covered it with a cloth. Had mold on top every time. With the bag, I've had none at all.