I really like "Albatross". It feels most like a TOS eps and would have been a damn fine one. And a really good McCoy story, too. Nice.
Of all ST eps where a crewmember is jailed or imprisoned for a crime, I like this one the best.
And yet "Slaver" is really good, too. A unique adventure without Kirk or the Enterprise and very nice to see Uhura and Sulu play major roles. Very good eps.
A tough call here. But I'll give it to "Albatross".