I am interested that no one is offering citations to back their assertions.

Some arguments are fairly well reasoned, but none seem conclusive because adequate references are not provided.

While one phrase may "seem" more correct, more widely used, than another, only statistical analysis can provide an accurate determination. Some statistically based examinations suggest that "all of a sudden" is used more frequently, but precise studies which reveal the distribution and use of the phrases in question are not cited.

Furthermore, grammatical arguments that have been presented are fairly technical, somewhat vague, and, again, do not offer referrals to well-credential sources.

I submit that using a definite article makes the phrase more specific and, therefore, more desirable.

Both "I was surprised by a sudden flash of light" and "I jumped at the sudden movement of her hand" make sense.

Perhaps there is a correllary with the phrase in question. Perhaps context most correctly determines which article should be used.

Thank you for your discussion.