As an instructor, I am often asked as to which Martial Arts style or discipline is the best.  I always conjure up a mental image of Harry Hill lining up a bout between Bruce Lee on one side and Alex Reid on the other (media perceptions of known martial artists being as well researched as they are).  But the truth is, that most people have no real idea of the difference between one martial art and another, other than what they might have seen in the media.  Therefore it is a fair question.  I personally believe it is more relevant to ask what it is the potential student wants from their time training in martial arts than it is to ask which is the better style.  There are suitable differences between most of the disciplines that should sway a potential students decision legitimately, but each art form also offers something that is unique to their discipline.  Not, as you might expect, is it with regards to secret techniques or Dim Mak moves (although this may also be the case) but, with the person who is the teacher.  The instructor, for me makes the art form.  An amazing instructor can make any art form seem magical and inspirational, whereas a poor one can make even the most exciting discipline a tedious activity.  They do say, when a student is ready, the teacher will appear.  
Or we can just decide this in a more acceptably mainstream way, 
"which martial art is better, lets find out, FIGHT!!!"