I read mostly at home and I read all but one kindle with no cover. The Oasis2 doesn't go in a cover at all anymore. Just to annoying after a while. I had the original, then got one of those snap in one and it was just too heavy. Much more comfortable out. I don't worry about it. I have no kids or dogs and always lay it face down. Its my most used right now. I also bought a basic recently and wont even bother every getting a cover for it. If I ever take it along, I'll just put it in a sleeve. But I don't really read much out and about.
My Oasis1 always stays in the cover. Mostly because the device battery is getting a bit up in age and I have 2 covers for it so can just flip through them before charging anything. It lives upstairs now and lasts forever as I don't grab it much.
My Voyage only lives in its cover now as I don't use it much. I can only use one kindle at a time after all.