Short lines give you a real sense of connection to your kite, sharpens your reflexes and hones skills. I use 30' x #90 as I chopped up a spare line set I had. I don't have any quad #50, well yet. I use the 13" handles. The short length makes it easier to muscle your kite if there is no wind. Don't just use it in light wind though, it is a real blast in normal wind, a complete hoot in higher wind! 3D work is so much fun and looks really trick too.
I would say that my 30's is my most used set. Probably use it 60% of the time.