If the mass spectrometry test gives you individual E1 and E2 values then it has the potential to be more accurate, if done right. But MS is tricky and when they mess it up the results can be way off—mine have been ridiculously wrong 30% of the time. On the other hand, the immunoassay-based estradiol tests are idiot proof and very reproducible, but they do cross-react with some other substances and can tend to read somewhat high—my results are about 5% higher than MS, and larger disparities are not uncommon.... why the liquid-c test may not be that great either...
There's no clear answer as to which is better. Best is to use both methods, if affordable, at least in the beginning. Having cross-calibrated the methods I am now comfortable using only the immunoassay tests, and Defy accepts them.