Look for versions that handle the era-specific slang (like "grass" or "behave yourself") well. Some American releases were actually partly re-dubbed in 1971 because the original dialogue was deemed too difficult for domestic audiences.
The 2000 remake is often criticized for being a "bland" rehash of the original. Get Carter | Rotten Tomatoes Get Carter subtitles Greek
When reviewing subtitles for it is important to first distinguish which film you are watching, as the legendary 1971 original starring Michael Caine and the 2000 remake with Sylvester Stallone offer very different experiences. Review: Get Carter (1971) – Greek Subtitles Look for versions that handle the era-specific slang