I consider those three the first-class episodes, too ("One of Our Planets Is Missing," "Yesteryear," and "The Time Trap").I love TAS. My favorite eps are One of Our Planets, Yesteryear, and Time Trap. All of which I would love to see turned into movies.
"Beyond the Farthest Star" isn't far behind. It's exciting and overall very good, and it has some outstanding parts, but I cringe when the alien electricity laughs maniacally.