Which is a nicer nickname for the name Melissa, Missy or Lissa?

I have used both nicknames. My family and relatives have called me Lissa, or Melissa ever since I can remember. My schoolmates in middle school started calling me Missy and it stuck all through out college. My co-workers know me as Melissa. I'd like to stick to one nickname, which one do you think is more attractive to people in general? I name says a lot about the person and so I'd like it to be a positive one.