Joking answer: Star Trek: The Next Generation season 1, but skip all episodes except "Code of Honor", which is the "best" in the franchise.
Serious Answer: DS9 season 1. Although it's less hopeful than the typical Trek in many senses, I think it still has that Trekian sense of ethics about it. Also, the characters are great, and the first season is much more watchable than TNG season 1.
But what about those kids in TOS who all joined a cult and murdered their parents for fun or something?