I'd say the best-looking computers were the M-5 in "The Ultimate Computer" and the Beta 5 in "Assignment Earth,"
What? No Rayna Capek from "Requiem for Methuselah" or Andrea ("Androida"?) from "What Are Little Girls Made Of?" Alice from "I, Mudd"?
I laughed out loud at that. How could I have missed those? They're easily the finest builds in all of Star Trek