You are better off taking the breath test.
The two systems are set up so that the mean alcohol concentration is measured and then 5 standard deviations are taken off to get the result which is printed out. Hence the result is not, "x mg per 100ml" but, "without a shadow of a doubt more than x mg/100ml". This avoids any legal arguments about measurement accuracy. If the SD was zero a person on the limit would score at the limit whether he took the breath test or the blood test. However, the breath test is inherently less precise and so the SD is bigger and effectively more gets taken off to produce the final reading. This is recognised as favouring the suspect who takes the breath test but is tolerated because the breath test is easier, cheaper and less messy to administer. A policeman can do it rather than a medical professional. In the UK two or more tests are done, separated by 2 hrs. You are not guilty till they get two consecutive results over the limit and they won't let you go till you give two consecutive specimens below the limit.
The limits, especially for commercial flying, are pretty low. It is a pain having to be careful about a couple of glasses of wine at dinner the night before, but is it worth your licence?