Mine are in dustbags (always) in a closet...and, OK, on a closet floor too as I need to remodel the closet. I don't stuff, as much as it's a good idea to keep their shape.
I don't keep the bag in a dustbag unless it's not in use. Whatever bag I'm using I'll just make sure it's in a safe place where my pets won't damage them. Any bag that's not being used is in their dust bag in my closet.
I stuff mine with the air pillows from Eluxury. It keeps them in shape nicely. I've tried t-shirts and towels, but you need like a million of them and they can look lumpy if they aren't packed right.
Stuffed and inside the dustbag except for the bags that I use. I do switch bags every couple of days depending on my mood I tried folding my speedy once and didnt like the crease. The crease evens out after a few days but it bothers me so I never folded it again.