It seems there may be some confusion or ambiguity in the query "isaidub 300 Spartans 2021 best." Let’s break down the key elements and provide a helpful, legally sound guide based on available information. The term "isaidub" does not appear to correspond to any official streaming platform, dubbing service, or film title. It could be a misspelling, a mix-up of terms, or a reference to a non-English resource (e.g., a dubbed version of a film in a specific language). However, no credible platform or service under this name is officially recognized as of 2021.