Perhaps I have a very strange perspective on linguistic issues, but please hear me out.

When speaking, my goal is not generally to sound educated, but to sound right. A generous application of the "Rock 'n' Roll Rule" means that a contentious phrasing like this one merits a closer look... in the song performance of 20th-century pop culture. After all, nobody defines what sounds to people right better than whoever's considered cool (and stayed that way, of course). And you have audio recordings of what was said (though it may be slurred... or shouted. Or growled).

A search for lyrics across a wide range of sites will turn up far more hits for "all of a sudden" than "all of the sudden". And if you listen to songs in the latter category, it is often the case that whoever transcribed those lyrics heard the words wrong. So conclusively, what seems right to the gods of rock (as well as country and a couple of other genres) is definitely the phrase "all of a sudden", regardless of what is actually correct.

One phrase I had to invent this rule for was "another thing coming" versus "another think coming". It turns out that the latter -- although it sounds wrong to me -- is actually the original, proper phrase. But... if the incorrect way is good enough for Judas Priest, I don't mind being incorrect, I suppose.

Naturally, one is permitted to come up with one's own manner of speaking, but for my purposes, the set of songs with transcribed lyrics gives me a pretty decent (searchable and quantifiable) corpus of casual speech, as opposed to print. Radio, TV, and film are not quite a searchable at present, unfortunately.