I don't really rank the star treks I like.
I used to, but then I find it just depends on what mood I'm in to what I like more, and then I'm constantly changing my rankings, and in the end it's just a go-nowhere thought process... they all have strengths and weaknesses.
I just have star trek shows I like, and star trek shows I dislike.
I like TOS,TNG,and DS9.
I dislike Voyager and the majority of Enterprise.
Beyond that, I find it impossible to rank which is my "favorite" or which is the "best"