I have seen some pictures of trans women where you can tell they have more masculine legs. But I don't think it has much to do with the question of whether the knees touch. It has more to do with their overall length compared to the torso (men's are comparatively short), the angle of the thighs (straighter for men; slanted outward for women), and the width of the hips (narrower for men). Musculature is also a factor -- women's muscles are simply not as defined most of the time. Fat has little to do with it, really.
Frankly, I think my legs are one of my better physical assets, and that's true for at least one other trans woman I know. A skirt, depending on the cut, can be a good way to show legs off and make them look longer, and often flatter a figure with narrower hips. If I want to look my best, I definitely prefer skirts or dresses. Heels too, if I can get over being self-consious about my height. Because of the way they alter your stance and lengthen the legs overall, heels just make legs loke more feminine.