Actually I don't think these episodes are very close in quality, despite the similarities you list. Dagger is far superior.
- I adore Dr Helen Noel, the sexiest woman ever to appear on TOS. She's also a little more active than most TOS eye candy. She kills that guy in the shield control room, and disables the shield.
- The byplay between them evokes life on board the Enterprise between missions ("At the Christmas party – ?"). In general I enjoy all the early s1 episodes where they paint a picture of an ongoing life around the Federation, even if the main story is not all that compelling.
- I like Morgan Woodward, even in this hammy role. As a kid I did not realize he was the same actor who later played Captain Tracey; but the first time I saw Omega Glory I knew Tracey was loony.
- The conversations between Kirk and Dr Adams are enjoyable, as Kirk's attitude evolves from utter respect thru embarrassed verification to suspicion to deadly enemy. There are some nice moments: a three-sided conversation including Dr Noel on the humane treatment of the insane; and a conversation via communicator with Spock where Dr Adams excuses himself from the room to give privacy.
- First mind meld!
There is a lot of interest here. And the ending commands some sober respect.
By contrast, Little Girls is merely creepy. The mental time bomb Kirk sets for his double (I'm sick of your half-breed interference!) is clever, and I love the various Ruk themes in the score. But there isn't a whole lot here. Nurse Chapel is much less interesting than Dr Noel – which is a shame, since she was a regular character and Dr Noel a one-shot – and Dr Korby is less interesting than Dr Adams.
I vote Dagger.