What level would an assistant professor be hired at, if applying to associate professor position at another institution?
Based on what I've heard and seen, most schools fall into the second pattern, with the first and third happening much less frequently. However, I've known all three possibilities to occur. Ultimately, there is no "most likely" or "least likely" option, as it really depends on the rules for tenure promotions at the individual school at which the applicant is being hired.