I keep many of my jackets on forms, it seems to be a great way to store and display my items. If not on a form or mannequin keep flat and not hung on any low quality hangers. I once did irreparable damage to a jacket by storing it on a cheap hanger and over time the leather deformed to the hanger shape and put bad dents in the shoulders. So yeah, on a form or laid flat is the best storage.

I once almost bought an a-2 for 250$ but passed on it. The seller kept it on a hanger and it ended up forming to it. It also had the metal stain on the inside and the shoulders were wearing out because the hanger wore through. If I can avoid any clothes on a hanger I do it. The only hangers I do use are wood.