That's most interesting, crew. I DO love Dagger of the Mind -- I love Morgan Woodward as Van Gelder (especially when he just tries to say his name) and of course Helen Noel is, by popular consensus, the most beautiful woman ever to appear on TOS (by a nose!) Tristan Adams is a terrific villain.
However, I have to vote for What Are Little Girls Made Of because Roger Korby (Michael Strong) is a more interesting villain, and he better represents the theme of technological immodesty. His hunger for immortality is a more interesting character motivation than Dr. Adams' brainwashing evil. It's a more subtle theme, to my mind. Little Girls is darker, moodier, with more jealousy, more romanticism, and more passion. (Speaking of Star trek women, Sherry Jackson sure gives Marianna Hill a run for her money!)
Korby remains a sympathetic character right up to the end when he hands Kirk his phaser weapon. I've been watching this episode for decades, and I'm picking up now on the way he says "Now do you understand?" every time he shows Kirk a new android cloning trick. Korby is talking technology. Kirk is talking morality.
It's as if you showed me your iphone and all the cool things it can do -- and you say "Now, do you understand?" And meanwhile the iphone is causing people to walk across streets without looking, or otherwise distracting a person from other things he should be doing (like making a living, being with one's children, etc).
The underlying theme of technological immodesty is ultimately more interesting than the old Cold War theme of brainwashing and mind control.
Little Girls by a nose. THANKS FOR SHARING YOUR VIEWS.
~ Mr Atoz