IMHO, the best was “A Taste of Armageddon”. The sets and costumes were embarrassingly cheezy, but the story was really good.
I saw a short interview of Star Trek’s prop director. He said their primary source of props was Paramount’s dumpsters. There was one scene in which he pointed out that the design on a wall was in fact plastic coasters.
They did have one advantage. No one really knew what a star ship should look like.