It depends on the context. If someone uses macOS or iOS, there is no choice of which screen reader you use, only VoiceOver on both platforms. There are alternatives to TalkBack on Android, but user numbers are comparatively low, suggesting that TalkBack is the de facto choice.
Windows is the exception, where there is a choice of screen readers; the built-in screen reader Narrator, plus NVDA or Jaws. Most people use Jaws or NVDA, but we have no data about how interchangeably people use them.
There's a considerable overhead involved in learning a new screen reader. NVDA, Jaws, and Narrator have many tens of keyboard commands at their disposal. Even though there are similarities, the differences are enough to make the learning curve more significant.
That said, it's not uncommon for people to use a backup screen reader for those times when their primary Windows screen reader fails. That doesn't mean people switch between one and the other completely, more that they're familiar enough with their backup screen reader to be able to use it to get themselves out of difficulties with their primary screen reader.