Which of the following contractions should not be used in formal transcripts?

The use of contractions in formal transcripts is typically avoided to maintain professionalism and clarity. Among the listed options, 'ain't' is particularly considered unprofessional and is generally not accepted in formal writing or transcription. This term lacks the level of formality needed for official documents and is often thought of as colloquial or nonstandard English.

In contrast, the other contractions like 'isn't,' 'doesn't,' and 'hasn't' are widely accepted in both written and spoken English. They are commonly used and can convey meanings without detracting from the formality of the text. Therefore, 'ain't' stands out as the contraction that should not be used in formal transcripts, reiterating the importance of maintaining a professional tone in transcription work.