They’re all fine. (Rectal is the most accurate, and armpit is the least accurate, if you really want to know.) What’s important to know is that the various methods can vary by a degree or so. Thus, don’t use a forehead thermometer and compare it to the reading from an ear thermometer. Stick with one thermometer and measure regularly so that you know when a reading is different from your normal temp.
Even temp readings between two of the same type of thermometers can be slightly different.
Its obviously ideal to have best accuracy and precision. But, precision (closeness of the readings to each other) is more important than accuracy.
Thanks. I had been wondering if part of the reason so many have “normal” temperature below 98.6 had to do with the type of thermometers most frequently used now compared to the types used fifty years ago.