I've always been very suspicious of leather bags. It seems that every time I come across a yard sale or flea market "find" of an old leather bag with cameras or lenses inside, they are ruined by extensive fungus. I suspect that the leather traps moisture and provides a yummy environment for mold/mildew organisms. In addition, leather bags are a good deal heavier than their fabric counterparts, an issue for this old geezer with a bad back and medium format cameras to tote.
Certainly I'm not adverse to spending some money on my bags (or any other photo trinkets), but if I do, it will be on a Billingham.