What is the difference between meccha and chou? I read this blog (https://toranomon-ls.com/what-is-the-difference-between-totemo-and-chou-and-meccha-in-japanese/) but it seems like they can be used interchangeably? Is there any actual difference, or certain situations that require a certain word?
超 (chō) is basically "super" or "ultra". While it can slangily modify words like うれしい, 欲しい and 頑張った in informal conversations, it is also a prefix used in academic terms, for example 超伝導 ("superconductivity"), 超長距離 ("ultradistance") and 超光速 ("superluminal").
めっちゃ is always used in informal situations. Although it's now common also around Tokyo, this is originally Kansai-dialect, and is more common in western parts of Japan.
めっちゃ and (slangy) 超 are grammatically interchangeable (they can modify both adjectives and verbs), but I feel めっちゃ is likely to be considered slightly more slangy, or "rougher", than 超, at least in eastern Japan. Friends of the younger generation would have no problem using either, but some people who are a bit more mature and gentle may avoid using めっちゃ.