As Jake said in his comment, both will be understood by a native speaker but the phrases he suggested ("are you ready yet?" and "you're still not ready?", or, in my experience, "have you finished getting ready?") do sound more natural and are more commonly used by native speakers (at least speakers in my area, the Northeast of America). Both of the phrases you mentioned, however, are correct, understandable, and interchangeable with one another.
I hope this helped, good luck with your studies!