If you want the best of the Original Series I would start with Forms of Things Unknown with David McCallum and Sir Cedric Hardwicke.
Thats a great episode which blends a time machine with elements of Diabolique.
Then the Zanti Misfits.
And two Great Robert Culps Architechts of Fear where hes convered into an Alien Monster and Demon with a Glass Hand.
My favorites anyways.