Pursuant to New Mexico law, a driver, merely by being licensed to drive in this state, implies his/her consent to submit to a breath test, a blood test, or both upon reasonable request from a law enforcement officer. I routinely get asked which is better (admittedly less often than I get asked how to get out of a DWI or DUI).
Pursuant to the rules of professional conduct, an attorney cannot inform someone how to break the law and get away with it --that succinctly addresses the latter. As far as the former...the short answer is that I trust blood tests more. What I will say is this: when a medical care professional is concerned about your health (which may be life or death-types of situations), he/she will draw and test your blood immediately. Hospitals do not have preliminary breath testing machines, much less the IR-8000 breath-alcohol testing machine that law enforcement officers use to test breath-alcohol content.
In addition, the results of a blood-alcohol test come back with one score whereas breath-alcohol tests require two tests, and thus come back with two results. I've seen breath-alcohol test results routinely vary by .02. To me, that's a big deal. Take for example, a breath-alcohol test card that comes back at a .09, and .07. Is that person at or above the legal (per se) limit of .08? Or, is that person below the legal limit?
The answer to that question depends not only on which score the fact-finder wants to believe, but which score, if either of them, is correct. Then, you throw in the fact that the machine has an acceptable margin of error of .02 in the first place, the possibility of false positives, radio frequency interference, breath-alcohol tube issues, calibration issues, source code issues, and other testing issues, and I don't know what to believe. A .12 breath-alcohol content may very well be a .08 in reality. The IR-8000 is not perfect. No machine is.
In DWI or DUI cases, it has been my finding that jurors prefer blood-alcohol tests. I'd estimate that for every 30 DWI or DUI cases I defend, one case will involve a police officer that tests my client's blood as opposed to breath.