"You're not" vs. "you ain't" [duplicate]

Possible Duplicate:
What does “ain't” mean?

What's the difference between "you're not" and "you ain't" ("...coming home")? I do realize that ain't is a contraction of are not — but still.

Which of the two forms should be used and when? Which is the most formal/informal?

Solution 1:

Ain't is informal, and it is a contraction for am not, are not, is not, has not, and have not. The last two were originally representing London dialect.

If it ain't broke, don't fix it.

They ain't got nothing to say.

The NOAD has a note about the use of ain't.

The use of ain't was widespread in the 18th century and is still perfectly normal in many dialects and informal contexts in both North America and Britain. Today, however, it does not form part of standard English and should not be used in formal contexts.

Solution 2:

You ain't is colloquial, certainly informal and probably not Standard English. You're not, like all contractions, is also colloquial, but occasionally found in writing. If you are a foreign learner, the best advice is to avoid contractions in writing until you feel confident about where to use them, but contractions in speech will make you sound more natural. But you might still want to avoid you ain't.