Perseus is the number one best mythological hero of all time for many reasons. Not only is he the son of Zeus (the king god of the universe) and killed a crazy mermaid called medusa (the one with snakes for hair), he also showed much compassion by helping out someone that he did not even know. He, Perseus, is much better than Jason because although he was trusted to receive gifts from the gods, he was given them in ready-to-use condition, unlike how Perseus had to figure out the best possible uses for his minimal objects that he received. And according to greekmythology.com, neither Jason nor Theseus are actually listed as mythological HEROES, although they were listed on the site, proving that the previously mentioned 'heroes' are not really heroes at all. As well as that, if you look at things in the sky, the only one of these three gods you will find currently represented as a constellation is, of course, the best hero, Perseus. As you can see, Perseus really is the best hero ever.
Perseus is not the best mythological greek hero because there are many other heroes in greek mythology who should receive credit for killing crazy evil stuff (chimera, sphinx, etc.) In fact, Hercules is named as one of the best heroes in greek mythology. He is well-known and had many victories during wars. But I do not understand if this is a question that will impact our society. We are talking about mythology which is also fiction. It is as if you are comparing that I like smarties but you like coffee crips more. It is not a relevant question because it is purely based on opinions. I may like one thing and you like another. I hope this has told you that it does not matter what I think about Perseus or what you think about him.
Not only did Perseus kill powerful mermaids like Medusa, he also managed to kill the Kraken (A super-powerful sea beast sent from the one and only sea god, Poseidon) with no help except for the deceased head of Medusa. This is a true act of heroic bravery because by doing so, Perseus ended up saving Andromeda (princess who was forced to death by the king and queen, her parents). Did Jason, Theseus, or Hercules do anything as brave as that? Ever? In comparison to Theseus, Theseus was selfish and did not care, at all, about his family. In contrast, Perseus was extremely loyal to his family, so much so that he, Perseus, risked his life to save his mother, Dana". Also, this is a debate, so it is always opinions being partially backed by questionable facts. Please, understand that I respect the partially heroic deeds committed by Hercules, but, he did not even do it by himself, as Perseus always had. This shows that he, Perseus, is the strongest and most heroic mythological god or goddess.
I am sorry. I cannot argue to that because I am just saying, it is fictional and therefore it is a matter of opinion. It does not matter about how many monsters you defeat in the world of Greek mythology, it is about your acts; Depending on how kind you are and if you helped make the world a better place. Isn't that what true heroism is?