I disclosed to several people at ACL 2014 that I have a secret list of best dressed people in the field, and got surprised that how many of them are really interested in it. Now it is official! This list is to recognize the efforts of who are being the eye-candies for us throughout the years. So there will be no worst dressed list. I defend everyone's right to wear whatever they want.
The criteria is threefold: good taste, appropriateness for occasions, consistency. This probably explains why there are more senior peoples on the list.
And apparently it is also biased by visibility (since I am not paying that much attention to what everyone is wearing).