If you're in the beginning of the process, pick a school you think you like. I picked Columbia, just to have an easy answer. Once you're more involved in the process, and start interviewing, you can pick a school that you have better chances at (i.e. one that you interviewed at).
You just need an answer, people don't really care, they just ask because it's the thing to do. It's not worth your time explaining that you will only get into a few of the 50 schools you applied to.