I shoot and eat a lot of hogs here and I would say there is no one correct answer. I've seen 100 lb. sows that I wouldn't feed to my dogs yet ate and enjoyed 200 lb. boars.
The main thing is to kill your hogs quickly so the animal doesn't have big load of fight or flight chemicals in the muscle. We always head shoot our hogs to put them down immediately. Second, fat hogs will be tastier than skinny ones. Third, process the animal as quickly as possible. In the summer I want the animal harvested, processed and in ice within 2 hours at most. In the winter you can go 4-5 hours without problem. Finally, soak your hog in some kind of brine solution for couple days. I normally change the solution every day and keep it soaking for 3-4 days until it stops bleeding out.
In general a fat sow of about 150lb. or less is best to eat.