I actually haven't given thought to whether they make me look dumpy or not - or, to be more honest, I tend to look dumpy in anything!
But I find loose, flowing skirts that come somewhere between my knees and my ankles by far the most comfortable summer skirt type. I have a couple that are less loose and come just below my knees with side slits, but I don't like them as well.
I almost never wear skirts or dresses in the winter. I walk a lot and don't find them practical (and I HATE pantyhose!). I do have a multipurpose black fake velvet skirt that comes nearly to my ankles with a modest slit in the back which I wear in the winter if I absolutely must wear a skirt. It's comfortable and very versatile since almost any kind of top can be worn with it. Add of course I have the required conservative dress with jacket in navy for wearing to job interviews. That comes to about mid-knee, I think. It's been a while since I needed to wear it. If I need to attend another job interview (God forbid!) I may need to buy something a bit more up-to-date!
Cheryl