The British series UFO should be number !. It was a very stylish metaphor for the Cold War - the aliens being the commies. The models and special effects were hokey -literally the same crew who did The Thunderbirds- the but acting was great and the writing was for adults. The Prisoner was another great show.
Gerry and Sylvia Anderson were truly pioneers in sci-fi effects, sets, models and wardrobe. You could tell they must have done backbreaking work on all of it.
Right down to making the ships, planes and vehicles looking “weathered” and worn from use.
The aliens were the creepiest looking things I had ever see as a kid. The episode where you saw them breathing liquids freaked me out. Then I found out they were really humans who were built with spare parts from other humans gave me nightmares. LOL