The MOST important is Validity, because if you can't believe that any value is true, any test is meaningless. Reliability is critical as well, because without it you really don't have a scientific test with which to test any hypothesis.
Validity is the most important. This is because, if a test instrument is not valid, then there's no need proceeding to seek for it's reliability. An instrument that is not valid has failed it's own purpose of design.
Validity is more important than reliability. Validity refers to the extent to which a measure accurately assesses the construct it intends to measure. While reliability refers to how consistently a method measures something.
While reliability remains an important psychometric property, validity ensures that the measure accurately captures the construct, allowing for valid evaluation. Without validity, even the most reliable measures may yield invalid or misleading results.