This is a hard question to answer because there are two possible interpretations to this question. The first is that is asking only for podcasts that have made a significant impact on your life. The second is to simply go through your podcasts and pick the one that has impacted your life the most, however small.

I'll answer according to the latter.

--Astonishing Legends has stretched my mind with the unexplained and opened me to the possibility of greater realities beyond what I immediately see.

--The Lawfare podcast (and Renato Mariotti's On Topic) has given me a (mostly) level headed and legal on-going discussion of the Trump/Russia affair. It has educated me a lot about our legal system and the value of the norms we keep in government.

--Hardcore History's series (basically audiobook length) on World War I has given me a sense about the tragedies and sufferings a previous generation experienced en mass that nobody has experienced today. Gives some perspective on life.

--Hello Internet is a podcast of pure fun that has expanded my hobbies and interests.

--Brain Software has help give me a better understanding of human psychology in the context of hypnosis and NLP.