I think it all depends on the type of midi, and the length as I just learned midi can be anywhere from just below the knee to just enough above the ankle to not look like your maxi shrunk. I also think just below the knee looks good on almost everyone. a classic look is a fuller skirt that is just below the knee with high boots for a winter look. Also just a few months ago there were many things on blogs about mid calf being hard to work with and, of course, the biggie about making legs look too short.
I am, though, having a problem with getting used to booties that are anywhere to about an inch above ankle to maybe 4 inches above ankle or so, worn with above the knee skirts, with all those inches of bare leg. Somehow this just doesn't sit well with me. I only see it on here, blogs, and pinterest. This look is not popular in my area,, but it is still very warm and sandals are still the way to go.