Even breathalyzer results taken minutes apart vary. This is a very inexact science, and breath/blood levels can vary significantly due to testing and sampling methodology. DUI attorneys have specialized knowledge of these factors, and should always be consulted in this type of case.
Blood tests are the most accurate as they measure alcohol in your bloodstream. Breath or urine tests use conversion rates to attempt to equate both of these tests to the blood test if they were taken at the same time. It is really isnt an exact science but the short answer to your question is blood is the most accurate and the variance rate of the other two will depend on your state's conversion rate. Talk to an attorney to discuss further. Good luck.
This refers to what is called a partition ratio, which varies from one person to another, and can even vary for the same person from one day to another. If you're facing DUI charges, consult with a locally experienced DUI attorney. Good luck.